librustc: Have coherence check Copy kind bounds when determining whether parameter substitutions could possibly unify. r=nmatsakis

Remove old syntax ext

r=brson

Closes #3788

Reverse the order of the results of pipes::stream

As per #3637.

This disallows using pointers to sneak around priv qualifiers.

Deeming this too small for review as well. Closes #3763

When a type error has already occurred, don't call ty::subst,
which may ICE due to the mismatch in the number of type params
involved.

I'm deeming this too small to review.

Closes #3680

The FIXME is an underlying issue (a core::at_str library) that this
doesn't address.

Conflicts:

	src/libstd/future.rs

Fix deriving for single-variant enums