This commit is part of a series that introduces a `std::thread` API to
replace `std::task`.

In the new API, `spawn` returns a `JoinGuard`, which by default will
join the spawned thread when dropped. It can also be used to join
explicitly at any time, returning the thread's result. Alternatively,
the spawned thread can be explicitly detached (so no join takes place).

As part of this change, Rust processes now terminate when the main
thread exits, even if other detached threads are still running, moving
Rust closer to standard threading models. This new behavior may break code
that was relying on the previously implicit join-all.

In addition to the above, the new thread API also offers some built-in
support for building blocking abstractions in user space; see the module
doc for details.

Closes #18000

[breaking-change]

We need to be sure to init thread_info before we init args for example because
args is grabbing locks which may entail looking at the local thread eventually.

There's always a fun time having two sets of standard libraries when testing!

Also removes:

* `std::task`
* `std::rt::task`
* `std::rt::thread`

Notes for the new API are in a follow-up commit.

Closes #18000

This commit removes the runtime bookkeeping previously used to ensure
that all Rust tasks were joined before the runtime was shut down.

This functionality will be replaced by an RAII style `Thread` API, that
will also offer a detached mode.

Since this changes the semantics of shutdown, it is a:

[breaking-change]

This commit merges the `rustrt` crate into `std`, undoing part of the
facade. This merger continues the paring down of the runtime system.

Code relying on the public API of `rustrt` will break; some of this API
is now available through `std::rt`, but is likely to change and/or be
removed very soon.

[breaking-change]

EnumSet lives on in libcollections so that librustc can still use it. This adds a direct dependency on libcollections to librustc and libserialize.

Should not be merged until https://github.com/rust-lang/rfcs/pull/509 is accepted.

All of these collections have already been moved to collect-rs where they will ideally be maintained and experimented with, or will be replaced by something better: https://github.com/Gankro/collect-rs/

[breaking-change]

r? @aturon @alexcrichton 

If you configure with `--disable-docs`, the `doc` directory does not get generated, so the
`cp -r doc dist/` step fails when you `make dist{,-tar-bins,-doc}` or `make install`.

followed by a semicolon.

This allows code like `vec![1i, 2, 3].len();` to work.

This breaks code that uses macros as statements without putting
semicolons after them, such as:

    fn main() {
        ...
        assert!(a == b)
        assert!(c == d)
        println(...);
    }

It also breaks code that uses macros as items without semicolons:

    local_data_key!(foo)

    fn main() {
        println("hello world")
    }

Add semicolons to fix this code. Those two examples can be fixed as
follows:

    fn main() {
        ...
        assert!(a == b);
        assert!(c == d);
        println(...);
    }

    local_data_key!(foo);

    fn main() {
        println("hello world")
    }

RFC #378.

Closes #18635.

[breaking-change]

---

Rebased version of #18958
r? @alexcrichton 
cc @pcwalton 

followed by a semicolon.

This allows code like `vec![1i, 2, 3].len();` to work.

This breaks code that uses macros as statements without putting
semicolons after them, such as:

    fn main() {
        ...
        assert!(a == b)
        assert!(c == d)
        println(...);
    }

It also breaks code that uses macros as items without semicolons:

    local_data_key!(foo)

    fn main() {
        println("hello world")
    }

Add semicolons to fix this code. Those two examples can be fixed as
follows:

    fn main() {
        ...
        assert!(a == b);
        assert!(c == d);
        println(...);
    }

    local_data_key!(foo);

    fn main() {
        println("hello world")
    }

RFC #378.

Closes #18635.

[breaking-change]

Windows dbghelp strips leading underscores from symbols, and I could not find a way to turn this off.  So let's accept  "ZN...E" form too.
Also, print PC displacement from symbols.  This is helpful in gauging whether the PC was indeed within the function displayed in the backtrace, or whether it just happened to be the closest public symbol in the module.

Closes #5988.
Closes #10176.
Closes #10456.
Closes #12744.
Closes #13264.
Closes #13324.
Closes #14182.
Closes #15381.
Closes #15444.
Closes #15480.
Closes #15756.
Closes #16822.
Closes #16966.
Closes #17351.
Closes #17503.
Closes #17545.
Closes #17771.
Closes #17816.
Closes #17897.
Closes #17905.
Closes #18188.
Closes #18232.
Closes #18345.
Closes #18389.
Closes #18400.
Closes #18502.
Closes #18611.
Closes #18783.
Closes #19009.
Closes #19081.
Closes #19098.
Closes #19127.
Closes #19135.

r? @nikomatsakis 

We discussed coercions for `if` and `match` expressions. `if` seems to work already, was there some specific behaviour which wasn't working?

If you configure with `--disable-docs`, the `doc` directory does not get generated, so
`cp -r doc dist/` fails when you `make dist{,-tar-bins,-doc}` or `make install`

Closes #19937.

Random improvements to the `std::vec` docs.

Signed-off-by: NPhilipp Gesang <phg@phi-gamma.net>

r? @Gankro @pczarn

On the [guide site](http://doc.rust-lang.org/guide.html#if) I was confused when I got to "5 If". It looked like "5 LF" in lowercase.

Changing the if to lowercase solves this problem. I know titles are all capitalized, but I think it makes sense in this case to keep it lowercase, since `if` is a reserved word. I'd also be open to making it ```    `if`   ``` but I'm not sure how that would look on the site.

Before:
![screen shot 2014-12-16 at 12 58 01](https://cloud.githubusercontent.com/assets/632942/5458866/cb34c006-8523-11e4-89ef-3a3964bcedfc.png)
After:
![screen shot 2014-12-16 at 12 58 14](https://cloud.githubusercontent.com/assets/632942/5458865/cb33c444-8523-11e4-8d95-d377ed583ed6.png)

Fix `make TAGS.emacs`.

@nikomatsakis has been complaining to me about this.  (I had not noticed since I drive `ctags` with a separate script.)

(Suitable for a rollup build.)