coro.compress: new boolean property - whether to compress the stack when evacuating it
coro.compressed: boolean ivar - has the evacuated stack been compressed?
sched.squish: zstack object holds compression context
sched._preserve_last(): optionally compress stack before evacuation
sched._restore(): uncompress if needed before restore
sched.compress(): compress an idle coro's stack

Require cython + pyrex to allow Shrapnel to be install via pip

Require cython + pyrex to allow Shrapnel to be install via pip (http://mail.python.org/pipermail/distutils-sig/2007-September/008204.html)

on aplib.

define __swap() with and without extra underscores to cover osx/mach