multiprocessing: Implement Pipe-alike.

Unfortunately, any Pipe used for parent/child child communication
needs to be registered with child Process. To get around that, would
need to keep global registry of Pipes, and that's bloat.
multiprocessing: Add dummy Pool implementation which doesn't really uses pool.
multiprocessing: Add trivial AsyncResult, not much async at all.
select: Add Epoll.close().
multiprocessing: Add AsyncResult.ready() with real async implementation.
multiprocessing: Add true async proof-test.
multiprocessing: Update metadata.
pickle: Add trivial pickle implementation using repr()/exec().