rustc::driver: Remove two @s
syntax::diagnostic: Remove unnecessary traits

This removes trait `handler` and `span_handler`,
and renames `HandlerT` to `Handler`, `CodemapT` to `SpanHandler`.
syntax::diagnostic: Remove @ from Emitter
syntax::codemap: Add static DUMMY_SP

It replaces `dummy_sp()`.
auto merge of #11255 : klutzy/rust/small-cleanup, r=pcwalton

This patchset removes some `@`s and unnecessary traits,
and replaces a function (`dummy_sp()`) returning constant value
by static variable.
Move task count bookeeping out of libstd

For libgreen, bookeeping should not be global but rather on a per-pool basis.
Inside libnative, it's known that there must be a global counter with a
mutex/cvar.

The benefit of taking this strategy is to remove this functionality from libstd
to allow fine-grained control of it through libnative/libgreen. Notably, helper
threads in libnative can manually decrement the global count so they don't count
towards the global count of threads. Also, the shutdown process of *all* sched
pools is now dependent on the number of tasks in the pool being 0 rather than
this only being a hardcoded solution for the initial sched pool in libgreen.

This involved adding a Local::try_take() method on the Local trait in order for
the channel wakeup to work inside of libgreen. The channel send was happening
from a SchedTask when there is no Task available in TLS, and now this is
possible to work (remote wakeups are always possible, just a little slower).
auto merge of #11212 : alexcrichton/rust/local-task-count, r=brson

For libgreen, bookeeping should not be global but rather on a per-pool basis.
Inside libnative, it's known that there must be a global counter with a
mutex/cvar.

The benefit of taking this strategy is to remove this functionality from libstd
to allow fine-grained control of it through libnative/libgreen. Notably, helper
threads in libnative can manually decrement the global count so they don't count
towards the global count of threads. Also, the shutdown process of *all* sched
pools is now dependent on the number of tasks in the pool being 0 rather than
this only being a hardcoded solution for the initial sched pool in libgreen.

This involved adding a Local::try_take() method on the Local trait in order for
the channel wakeup to work inside of libgreen. The channel send was happening
from a SchedTask when there is no Task available in TLS, and now this is
possible to work (remote wakeups are always possible, just a little slower).
Parse macro_crate!
Load macro crates

We don't actually do anything with them yet.
Load macros from external crates!
Switch from macro_crate! to #[phase(syntax)]
Pull CrateLoader out of phase_2

This will allow rustpkg to use a custom CrateLoader that can track down
dependencies.
Properly unload macro crates

There's some unfortunate use of RefCell due to unfortunate use of @mut
:(
Feature gate #[phase()]
Integrate Rustpkg crate installation
Switch from magic name to #[macro_registrar]