syntax: allow `trace_macros!` and `log_syntax!` in item position.

Previously

    trace_macros!(true)
    fn main() {}

would complain about `trace_macros` being an expression macro in item
position. This is a pointless limitation, because the macro is purely
compile-time, with no runtime effect. (And similarly for log_syntax.)

This also changes the behaviour of `trace_macros!` very slightly, it
used to be equivalent to

    macro_rules! trace_macros {
        (true $($_x: tt)*) => { true };
        (false $($_x: tt)*) => { false }
    }

I.e. you could invoke it with arbitrary trailing arguments, which were
ignored. It is changed to accept only exactly `true` or `false` (with no
trailing arguments) and expands to `()`.
native: Fix a possible deadlock in spawn

The OSX bots have been deadlocking recently in the rustdoc tests. I have only
been able to rarely reproduce the deadlock on my local setup. When reproduced,
it looks like the child process is spinning on the malloc mutex, which I
presume is locked with no other threads to unlock it.

I'm not convinced that this is what's happening, because OSX should protect
against this with pthread_atfork by default. Regardless, running as little code
as possible in the child after fork() is normally a good idea anyway, so this
commit moves all allocation to the parent process to run before the child
executes.

After running 6k iterations of rustdoc tests, this deadlocked twice before, and
after 20k iterations afterwards, it never deadlocked. I draw the conclusion that
this is either sweeping the bug under the rug, or it did indeed fix the
underlying problem.
std: Add an I/O reader method to fill a buffer

I've found a common use case being to fill a slice (not an owned vector)
completely with bytes. It's posible for short reads to happen, and if you're
trying to get an exact number of bytes then this helper will be useful.
rand: Use fill() instead of read()

It's possible for a reader to have a short read, and there's no reason the task
should fail in this scenario. By using fill(), this has a stronger guarantee
that the buffer will get filled with data.
Get rid of @Cell
Implement vtable support for autoderef.
Closes #13042.
auto merge of #13085 : edwardw/rust/saddest-cell, r=cmr
Implement cross-crate support for autoderef.
Closes #13044.
auto merge of #13087 : eddyb/rust/fix-autoderef, r=cmr

Implements vtable support for generic Deref impls with trait bounds.
Also fixes cross-crate inlining when using autoderef.
Some cleanup in std::io::buffered

`Vec` is now used for the internal buffer instead of `~[]`. Some module
level documentation somehow ended up attached to `BufferedReader` so I
fixed that as well.
Change types T,U to R (recv), S (sender) in libsync/comm.rs
make std::managed private

This removes two tests built on `managed::refcount`, but these issues
are well-covered elsewhere for non-managed types.
auto merge of #13089 : thestinger/rust/managed, r=Aatch

This removes two tests built on `managed::refcount`, but these issues
are well-covered elsewhere for non-managed types.
use TotalEq for HashMap

Closes #5283
auto merge of #13088 : thestinger/rust/hashmap, r=cmr

Closes #5283
iter: remove `to_owned_vec`

This needs to be removed as part of removing `~[T]`. Partial type hints
are now allowed, and will remove the need to add a version of this
method for `Vec<T>`. For now, this involves a few workarounds for
partial type hints not completely working.
auto merge of #13090 : thestinger/rust/iter, r=Aatch

This has been rendered obsolete by partial type hints. Since the `~[T]`
type is in the process of being removed, it needs to go away.
Register new snapshots
auto merge of #13092 : sfackler/rust/buffer-vec, r=thestinger

`Vec` is now used for the internal buffer instead of `~[]`. Some module
level documentation somehow ended up attached to `BufferedReader` so I
fixed that as well.
rustc: Change the filename of compressed bitcode

Fixes #12992
Store compressed bitcode files in rlibs with a different extension. Compression doesn't interfere with --emit=bc.
Regression test compares outputs.