Throwing in upcall_fail ends up running lots of code in the red zone. To avoid
it we have the personality function figure out which stack it's on and switch
as needed.

rust_task is using the word limit it two ways, so one has to change.

When unwinding through __morestack the stack limit in the TLS is invalidated
and must be reset. Instead of actually landing at __morestack we're
just going to make all our Rust landing pads call upcall_reset_stack_limit,
which will find the stack segment that corresponds to the current stack
pointer and put the limit in the TLS.

Also massively expand the stack segment red zone to make more room for the
dynamic linker. Will fix in the future.

to char[16], not struct{long,long}

Sucks, but otherwise there are races when one task drops the refcount to zero
followed by another bumping it again

rustc: Port the fn and obj traversal logic over from the GC branch. Doesn't actually do anything yet due to lack of support in trans.

The failure will basically go 'through' the dead parent and continue
propagating the failure (as if the child was reparented).

When a task fails, we will throw an exception, then catch it at the bottom of
the stack.

On Windows we don't do this yet because the exception doesn't propagate
correctly.

No cleanups yet.

Issue #236

The motivation here is that the bottom of each stack needs to contain a C++
try/catch block so that we can unwind. This is already the case for main, but
not spawned tasks.

Issue #236

Removed trans_comm.rs from the compiler. Updating aio/sio to work with the new chan and port system, started on a networking module for the standard library.

This is the new way to refer to tasks in rust-land. Currently all they
do is serve as a key to look up the old rust_task structure. Ideally
they won't be ref counted, but baby steps.