Incoming

This lets us pass them to generic functions.

(basically a stripped-down version of comm, and a "driver" that
constructs a new port)

This allows destructors to be inlined, which is necessary since
classes can have both ty params and destructors.

And replace trans::common::block_parent with option<block>. To handle
the recursive self-reference in the block_ class, I had to add a
newtype-like enum "block" which is equivalent to @block_ -- which due
to an interaction with borrowck, resulted in having to change a few
functions in trans::base to take their block argument in ++ mode,
irritatingly enough (but not that irritatingly, since we're supposed to
get rid of modes).

This doesn't seem to show up anywhere else in the test suite, even
though it's supposed to be legal.

Closes #2550

Doing builds outside of the cwd is breaking rustc's logic for
locating crates in ./.cargo/lib.

Ideally, cargo would not be changing directories at all.

Conflicts:
	src/cargo/cargo.rs