rt::io: Add Bytes iterator for Reader

An iterator that simply calls `.read_bytes()` each iteration.

I think choosing to own the Reader value and implementing Decorator to
allow extracting it is the most generically useful. The Reader type
variable can of course be some kind of reference type that implements
Reader.
Raise the file descriptor limits when running compiletest

We already do this for libstd tests automatically, and compiletest runs into the
same problems where when forking lots of processes lots of file descriptors are
created. On OSX we can use specific syscalls to raise the limits, in this
situation, though.

Closes #8904
Fix inner statics having the same symbol name

Before, the path name for all items defined in methods of traits and impls never
took into account the name of the method. This meant that if you had two statics
of the same name in two different methods the statics would end up having the
same symbol named (even after mangling) because the path components leading to
the symbol were exactly the same (just __extensions__ and the static name).

It turns out that if you add the symbol "A" twice to LLVM, it automatically
makes the second one "A1" instead of "A". What this meant is that in local crate
compilations we never found this bug. Even across crates, this was never a
problem. The problem arises when you have generic methods that don't get
generated at compile-time of a library. If the statics were re-added to LLVM by
a client crate of a library in a different order, you would reference different
constants (the integer suffixes wouldn't be guaranteed to be the same).

This fixes the problem by adding the method name to symbol path when building
the ast_map. In doing so, two symbols in two different methods are disambiguated
against.
Remove __extensions__ in names for a "pretty name"

As with the previous commit, this is targeted at removing the possibility of
collisions between statics. The main use case here is when there's a
type-parametric function with an inner static that's compiled as a library.
Before this commit, any impl would generate a path item of "__extensions__".
This changes this identifier to be a "pretty name", which is either the last
element of the path of the trait implemented or the last element of the type's
path that's being implemented.  That doesn't quite cut it though, so the (trait,
type) pair is hashed and again used to append information to the symbol.

Essentially, __extensions__ was removed for something nicer for debugging, and
then some more information was added to symbol name by including a hash of the
trait being implemented and type it's being implemented for. This should prevent
colliding names for inner statics in regular functions with similar names.
Correctly determine OS to xfail in cross build
Modernise some Vim syntax highlighting.

- Remove highlighting of ``L"..."`` (obsolete syntax)
- Remove backslash at end of line being a line continuation always
  (obsolete syntax; this only affects comments, actually)
- Add highlighting for backslash at end of line and leading whitespace
  on the following line inside a string (a genuine line continuation)
Update a handful of keywords highlighted in Vim.

I added a few and removed a few and corrected a couple, all with
reference to the prelude. It ends up a slightly arbitrary decision
precisely what ends up in and what doesn't, unfortunately.
Highlight everything in the prelude in Vim.

This is a rather more extensive change than the last, but *ever* so much
easier to maintain reasonably, as there's then something to track
directly.
Update highlighting for prelude changes.
rt::io: Rename Bytes to ByteIterator and add note about iteration
Rename MutexArc access methods to unsafe_access
Add a safe implementation of MutexArc::access* methods

Current access methods are nestable and unsafe. This patch renames
current methods implementation - prepends unsafe_ - and implements 2 new
methods that are both safe and un-nestable.

Fixes #7473
Fixed docs and styles
Added ToStr impl for char
Changed ToStr impl for Ascii
Silence fo+=j error for users of Vim < 7.3.541.
Test and document escaping on format!()
auto merge of #8942 : novalis/rust/fmt, r=alexcrichton
Move llvm into the artifacts build directory
auto merge of #8943 : alexcrichton/rust/issue-8904, r=brson

We already do this for libstd tests automatically, and compiletest runs into the
same problems where when forking lots of processes lots of file descriptors are
created. On OSX we can use specific syscalls to raise the limits, in this
situation, though.

Closes #8904
Raise errors on format strings with unmatched `}`

Otherwise extra stuff after a lone '}' character is simply ignored, which is
very bad.

Closes #8938