Need this for building istrs

This leaves syntax::ast just defining the AST, which strikes me as somewhat
nicer

The syntax is

    alt x {
        mypat where mycond { ... }
    }

The condition may refer to any of the variables bound by the pattern.
When a guard fails, pattern-matching continues with the next pattern.

Closes #857

This is not currently necessary, but will be, when I land the new ivec
representation.

(I'll be using this for type-needs-copy-glue in the near future.)

Since they are now passed by pointer, this is no longer a problem

Type handles are uints, passing them by reference only causes
unnecessary spilling.

Also, give copy_val and move_val a more sane return type.

This makes it easier for the caller to optimize the take/drop away for
temporary values, and opens up new possibilities for alias handling.

Breaks tail calls.

If we lose tail calls, this is possible. It simplifies things a lot.

Direct motivation: We want ivecs with pointers pointing into
themselves. When copying those, the pointers have to be adjusted. It
is impossible to this when copying them with Load/Store.

These may already be defined by other includes. Hopefully puts out the windows
fire.

Doing so contradicts the locking order used everywhere else and causes
deadlocks.

Un-XFAIL task-perf-spawnalot

Closes #854

rustc: Introduce ABI versioning so we can change value representations without breaking the compiler

This changes the indexing syntax from .() to [], the vector syntax from ~[] to
[] and the extension syntax from #fmt() to #fmt[]

Put out the darwin fire for real

This reverts commit 09f4cd90.

Try again to put out the darwin tinderbox

This reverts commit d09b421d.

Try to put out darwin tinderbox fire

rt: Split out shapes into rust_shape.cpp and rust_shape.h so that shape code can be written outside of rust_shape.cpp