extra::test: handle slow benchmarks more gracefully.

This makes sure we always run benchmarks even if they are predicted to
take a long time, so that we have some non-zero time to display
(although the error bars may be huge for particularly slow benchmarks).

Fixes #9532.
Check more live Path nodes in dead-code pass
Dead-code pass now marks and warns foreign items
Suppress warnings in run-pass tests
Fix #10754 - `std::run` functions fail after io_error

The problem was that std::run::Process::new() was unwrap()ing the result
of std::io::process::Process::new(), which returns None in the case
where the io_error condition is raised to signal failure to start the
process.

Have std::run::Process::new() similarly return an Option<run::Process>
to reflect the fact that a subprocess might have failed to start. Update
utility functions run::process_status() and run::process_output() to
return Option<ProcessExit> and Option<ProcessOutput>, respectively.

Various parts of librustc and librustpkg needed to be updated to reflect
these API changes.

closes #10754
auto merge of #10870 : ktt3ja/rust/issue-10865, r=alexcrichton

Fix #10865 and #10939.
auto merge of #10936 : cadencemarseille/rust/issue-10754-std-run-unwrap-on-None, r=alexcrichton

The problem was that std::run::Process::new() was unwrap()ing the result
of std::io::process::Process::new(), which returns None in the case
where the io_error condition is raised to signal failure to start the
process.

Have std::run::Process::new() similarly return an Option\<run::Process\>
to reflect the fact that a subprocess might have failed to start. Update
utility functions run::process_status() and run::process_output() to
return Option\<ProcessExit\> and Option\<ProcessOutput\>, respectively.

Various parts of librustc and librustpkg needed to be updated to reflect
these API changes.

closes #10754
auto merge of #10952 : huonw/rust/1ms-bench, r=cmr

This makes sure we always run benchmarks even if they are predicted to
take a long time, so that we have some non-zero time to display
(although the error bars may be huge for particularly slow benchmarks).

Fixes #9532.
Add "proc" as keyword to emacs mode
auto merge of #10968 : MicahChalmer/rust/emacs-proc-keyword, r=metajack
auto merge of #10932 : alexcrichton/rust/feature-update, r=cmr
Rewrite std::comm

* Streams are now ~3x faster than before (fewer allocations and more optimized)
    * Based on a single-producer single-consumer lock-free queue that doesn't
      always have to allocate on every send.
    * Blocking via mutexes/cond vars outside the runtime
* Streams work in/out of the runtime seamlessly
* Select now works in/out of the runtime seamlessly
* Streams will now fail!() on send() if the other end has hung up
    * try_send() will not fail
* PortOne/ChanOne removed
* SharedPort removed
* MegaPipe removed
* Generic select removed (only one kind of port now)
* API redesign
    * try_recv == never block
    * recv_opt == block, don't fail
    * iter() == Iterator<T> for Port<T>
    * removed peek
    * Type::new
* Removed rt::comm
Fallout of rewriting std::comm
Fixes from review I'll rebase later
Fix select, will rebase into first commit later
std: Introduce a Runtime trait

This trait is used to abstract the differences between 1:1 and M:N scheduling
and is the sole dispatch point for the differences between these two scheduling
modes.

This, and the following series of commits, is not intended to compile. Only
after the entire transition is complete are programs expected to compile.
std: Introduce an unstable::stack module

This module will be used to manage the OS-specific TLS registers used to specify
the bounds of the current rust stack (useful in 1:1 and M:N)
std: Delete rt::test

This module contains many M:N specific concepts. This will no longer be
available with libgreen, and most functions aren't really that necessary today
anyway. New testing primitives will be introduced as they become available for
1:1 and M:N.

A new io::test module is introduced with the new ip4/ip6 address helpers to
continue usage in io tests.
std: Introduce std::sync

For now, this moves the following modules to std::sync

* UnsafeArc (also removed unwrap method)
* mpsc_queue
* spsc_queue
* atomics
* mpmc_bounded_queue
* deque

We may want to remove some of the queues, but for now this moves things out of
std::rt into std::sync
std: Expose that LocalIo may not always be available

It is not the case that all programs will always be able to acquire an instance
of the LocalIo borrow, so this commit exposes this limitation by returning
Option<LocalIo> from LocalIo::borrow().

At the same time, a helper method LocalIo::maybe_raise() has been added in order
to encapsulate the functionality of raising on io_error if there is on local I/O
available.