Before:
````
test.rs:3:21: 3:30 error: expected constant integer for repeat count but found variable
test.rs:3             let a = ~[0, ..n]; //~ ERROR expected constant integer for repeat count but found variable
                              ^~~~~~~~~
````

After:
````
test.rs:3:27: 3:28 error: expected constant integer for repeat count but found variable
test.rs:3             let a = ~[0, ..n]; //~ ERROR expected constant integer for repeat count but found variable
                                     ^
````

minor little performance issue - the vector and string implementations of TotalOrd turn out badly without explicitly inlining this

Good morning,

It's taken a long time, but I finally am almost done freeing libsyntax of `vecs_implicitly_copyable` in this pull request, but I'm running into some issues. I've confirmed that all but the last commit (which only disables `vecs_implicitly_copyable` pass the `check` tests. The last commit errors with this message, which makes no sense to me:

```
/Users/erickt/rust/rust/src/libcore/num/f32.rs:35:37: 35:43 error: expected `,` but found `=`
/Users/erickt/rust/rust/src/libcore/num/f32.rs:35         pub pure fn $name($( $arg : $arg_ty ),*) -> $rv {
                                                                                       ^~~~~~
```

and this stack trace:

```
#1  0x00000001000b059b in sys::begin_unwind_::_a923ca4ae164c::_06 ()
#2  0x00000001000b0542 in sys::begin_unwind::anon::anon::expr_fn_13876 ()
#3  0x00000001000048a1 in sys::begin_unwind::_8ec273289fc0adc0::_06 ()
#4  0x00000001005df999 in diagnostic::__extensions__::meth_7941::span_fatal::_efdf2d14612d79ec::_06 ()
#5  0x0000000100682d48 in parse::parser::__extensions__::meth_16938::fatal::_8aa3239426747a3::_06 ()
#6  0x00000001006850b8 in parse::common::__extensions__::meth_17005::expect::_d3604ec6c7698d5f::_06 ()
#7  0x00000001006b59f1 in parse::common::__extensions__::parse_seq_to_before_end_17860::_48c79835f9eb1011::_06 ()
#8  0x00000001006a50f7 in parse::parser::__extensions__::meth_17606::parse_fn_decl::_14f3785fe78967d::_06 ()
#9  0x00000001006b6f59 in parse::parser::__extensions__::meth_17987::parse_item_fn::_8a6be529cf7b2ca5::_06 ()
#10 0x00000001006ac839 in parse::parser::__extensions__::meth_17761::parse_item_or_view_item::_bfead947d6dd7d25::_06 ()
#11 0x00000001006c8b8f in parse::parser::__extensions__::meth_18364::parse_item::_96b54e33f65abe76::_06 ()
#12 0x000000010076179f in ext::tt::macro_rules::add_new_extension::generic_extension::anon::anon::expr_fn_23365 ()
#13 0x000000010072e793 in ext::expand::expand_item_mac::_a4f486c4465cfb1b::_06 ()
#14 0x00000001007b5ad3 in __morestack ()
```

There also a bunch of new warnings that I haven't cleaned up yet: https://gist.github.com/erickt/5048251.

@nikomatsakis thought there might be some scary bug in the parser caused by moving a vector in the parser instead of copying it, which is why I'm filing this pull request before it's ready. Thanks for any help!

This allows `TreeMap`/`TreeSet` to fully express their requirements and reduces the comparisons from ~1.5 per level to 1 which really helps for string keys.

I also added `ReverseIter` to the prelude exports because I forgot when I originally added it.

The fix is straight-forward, but there are several changes
while fixing the issue.

1) disallow `mut` keyword when making a new struct

In code base, there are following code,

```rust
struct Foo { mut a: int };
let a = Foo { mut a: 1 };
```

This is because of structural record, which is
deprecated corrently (see issue #3089) In structural
record, `mut` keyword should be allowd to control
mutability. But without structural record, we don't
need to allow `mut` keyword while constructing struct.

2) disallow structural records in parser level
This is related to 1). With structural records, there
is an ambiguity between empty block and empty struct
To solve the problem, I change parser to stop parsing
structural records. I think this is not a problem,
because structural records are not compiled already.

Misc. issues

There is an ambiguity between empty struct vs. empty match stmt.
with following code,

```rust
match x{} {}
```

Two interpretation is possible, which is listed blow

```rust
match (x{}) {} //  matching with newly-constructed empty struct
(match x{}) {}  //  matching with empty enum(or struct) x
                //  and then empty block
```

It seems that there is no such code in rust code base, but
there is one test which uses empty match statement:
https://github.com/mozilla/rust/blob/incoming/src/test/run-pass/issue-3037.rs

All other cases could be distinguished with look-ahead,
but this can't be. One possible solution is wrapping with
parentheses when matching with an uninhabited type.

```rust
enum what { }
fn match_with_empty(x: what) -> ~str {
    match (x) { //use parentheses to remove the ambiguity
    }
}
```

- Removed space between struct name and parentheses
- Fixed indentation of the rest of the file (missing end)
- Don't print parentheses for structs with no fields
- Added test

Moving them out of the way so the new scheduler code can occupy core::rt.

I have seen a few people confused on how to explicitly instantiate generic functions, since the syntax differs from C++'s and C#'s, which is probably where most people asking questions about generic functions are coming from. The only use of the `::<T>` syntax in the reference right now is in the section on paths, which is possibly not where someone trying to find out about generic functions is going to start looking. The tutorial doesn't mention it at all, but I think it's all right to make the reference a tiny bit more redundant and avoid stuffing the tutorial with syntax details.

----

The "Generic functions" subsection mentions that generic functions are instantiated based on context, so let's also mention right away (with a link to the #paths section) that an explicit form is available.

This also adds an example that explicitly instantiates a generic function to the function call expression section.

Before:
````
test.rs:3:21: 3:30 error: expected constant integer for repeat count but found variable
test.rs:3             let a = ~[0, ..n]; //~ ERROR expected constant integer for repeat count but found variable
                              ^~~~~~~~~
````

After:
````
test.rs:3:27: 3:28 error: expected constant integer for repeat count but found variable
test.rs:3             let a = ~[0, ..n]; //~ ERROR expected constant integer for repeat count but found variable
                                     ^
````

This adds a few words about unit-like struct types (`struct Foo;`) in the sections for `struct` items, structure expressions and structure types (and fixes an adjacent typo or two). The added text is at the same time triply redundant because of how the sections are split and rather brief because I don't think there's that much to say about field-less structs without digressing into `impl`s and generic functions and whatnot, but it's probably better than nothing for a start.

The added arm for the grammar of struct expressions is really awkward. It's just

    | expr_path

which is clearly not unambiguously a struct expression, but it didn't feel right not to add anything to the grammar chunk (and I can't tell whether the arm for enum-like structs is somehow unambiguous with regular enum expressions, either). Is this okay?

I'm wary of editing the offical-looking things like the contribution policy, but I hope fixing typos/the sentence structure is okay.

This changes various type_names to TypeNames and fixes the example for `tcp::accept` that was still using the old `match` syntax and `{|args| ...}` closures.

The `accept` example was fairly outdated. I was just going to stay away from all the IO things until the scheduler revamp lands, but `accept` is probably one of the obvious starting points for networking stuff for a learner, and I don't want to get in the way of anyone's enthusiasm.

Doesn't touch non-comment lines, so I hope I will get away without learning about unit tests. It doesn't seem like the test system is set up to extract tests from doc comments right now.

r?

This probably isn't controversial, but I want somebody else to sign off on it.

- Removed space between struct name and parentheses
- Fixed indentation of the rest of the file (missing end)
- Don't print parentheses for structs with no fields
- Added test

Also, rename the OptVec-to-vector conversion method to
opt_vec::take_vec() and convert from a method into a fn
because I fear strange bugs.

The "Generic functions" subsection mentions that generic functions are
instantiated based on context, so let's also mention right away (with a
link to the #paths section) that an explicit form is available.

This also adds an example to the function call expression section that
explicitly instantiates a generic function.

Doesn't touch non-comment lines. This changes various type_names to TypeNames
and fixes the example for `tcp::accept` that was still using the old
`match` syntax and `{|args| ...}` closures.

core: Address XXX, make static constants for strings used when stringify...