Many people will be very confused that their debug! statements aren't working
when they first use rust only to learn that they should have been building with
`--cfg debug` the entire time. This inverts the meaning of the flag to instead
of enabling debug statements, now it disables debug statements.

This way the default behavior is a bit more reasonable, and requires less
end-user configuration. Furthermore, this turns on debug by default when
building the rustc compiler.

This is for consistency in naming conventions.

- ``std::num::Float::NaN()`` is changed to ``nan()``;
- ``std::num::Float.is_NaN()`` is changed to ``is_nan()``; and
- ``std::num::strconv::NumStrConv::NaN()`` is changed to ``nan()``.

Fixes #9319.

Some minor api and doc adjustments

This is the second of two parts of #8991, now possible as a new snapshot
has been made. (The first part implemented the unreachable!() macro; it
was #8992, 6b7b8f26.)

``std::util::unreachable()`` is removed summarily; any code which used
it should now use the ``unreachable!()`` macro.

Closes #9312.

Closes #8991.

This is more consistent with other parts of the language and it also makes it
easier to use in situations where format string is massive.

This commit adds support for `\0` escapes in character and string literals.

Since `\0` is equivalent to `\x00`, this is a direct translation to the latter
escape sequence. Future builds will be able to compile using `\0` directly.

Also updated the grammar specification and added a test for NUL characters.

Since 3b6314c3 the pretty printer seems to only print trait bounds for
`ast::ty_path(...)`s that have a generics arguments list. That seems
wrong, so let's always print them.

Closes #9253, un-xfails test for #7673.

If a static is flagged as address_insignificant, then for LLVM to actually
perform the relevant optimization it must have an internal linkage type. What
this means, though, is that the static will not be available to other crates.
Hence, if you have a generic function with an inner static, it will fail to link
when built as a library because other crates will attempt to use the inner
static externally.

This gets around the issue by inlining the static into the metadata. The same
relevant optimization is then applied separately in the external crate. What
this ends up meaning is that all statics tagged with #[address_insignificant]
will appear at most once per crate (by value), but they could appear in multiple
crates.

This should be the last blocker for using format! ...

These really should have been marked xfail-win32, but that doesn't exist, so xfail-fast it is.

Closes #2074.
Closes #5008.
Closes #7519.
Closes #7673.
Closes #7770.
Closes #8171.

Closes #4208

Split up test function a bit

A SendStr is a string that can hold either a ~str or a &'static str.
This can be useful as an optimization when an allocation is sometimes needed but the common case is statically known.

Possible use cases include Maps with both static and owned keys, or propagating error messages across task boundaries.

SendStr implements most basic traits in a way that hides the fact that it is an enum; in particular things like order and equality are only determined by the content of the wrapped strings.

Replaced std::rt:logging::SendableString with SendStr
Added tests for using an SendStr as key in Hash- and Treemaps

In #8185 cross-crate condition handlers were fixed by ensuring that globals
didn't start appearing in different crates with different addressed. An
unfortunate side effect of that pull request is that constants weren't inlined
across crates (uint::bits is unknown to everything but libstd).

This commit fixes this inlining by using the `available_eternally` linkage
provided by LLVM. It partially reverts #8185, and then adds support for this
linkage type. The main caveat is that not all statics could be inlined into
other crates. Before this patch, all statics were considered "inlineable items",
but an unfortunate side effect of how we deal with `&static` and `&[static]`
means that these two cases cannot be inlined across crates. The translation of
constants was modified to propogate this condition of whether a constant
should be considered inlineable into other crates.

Closes #9036

Remove these in favor of the two traits themselves and the wrapper
function std::from_str::from_str.

Add the function std::num::from_str_radix in the corresponding role for
the FromStrRadix trait.

While they may have the same name within various scopes, this changes static
names to use path_pretty_name to append some hash information at the end of the
symbol. We're then guaranteed that each static has a unique NodeId, so this
NodeId is as the "hash" of the pretty name.

Closes #9188

The cases they test are well covered in the `std::iter` tests.

Use the iterator version instead of the old uint::/int::range_step
functions.

While usage of change_dir_locked is synchronized against itself, it's not
synchronized against other relative path usage, so I'm of the opinion that it
just really doesn't help in running tests. In order to prevent the problems that
have been cropping up, this completely removes the function.

All existing tests (except one) using it have been moved to run-pass tests where
they get their own process and don't need to be synchronized with anyone else.

There is one now-ignored rustpkg test because when I moved it to a run-pass test
apparently run-pass isn't set up to have 'extern mod rustc' (it ends up having
linkage failures).

The normal unit tests cannot change the current working directory because it
messes with the other tests which depend on a particular working directory.

Closes #9123

Options are not numeric types, so it doesn't make sense for them to
implement Zero.

Vecs are not numeric types, so it doesn't make sense for them to
implement Zero.

Closes #9119

The purpose of this macro is to further reduce the number of allocations which
occur when dealing with formatting strings. This macro will perform all of the
static analysis necessary to validate that a format string is safe, and then it
will wrap up the "format string" into an opaque struct which can then be passed
around.

Two safe functions are added (write/format) which take this opaque argument
structure, unwrap it, and then call the unsafe version of write/format (in an
unsafe block). Other than these two functions, it is not intended for anyone to
ever look inside this opaque struct.

The macro looks a bit odd, but mostly because of rvalue lifetimes this is the
only way for it to be safe that I know of.

Example use-cases of this are:

* third-party libraries can use the default formatting syntax without any
  forced allocations
* the fail!() macro can avoid allocating the format string
* the logging macros can avoid allocation any strings