Adding special C code that allows redis's async client to use goroutines
and poll (on Linux) to check the status of file descriptors. These
goroutines replace the functionality of other C libraries like libevent.

These changes fixes some problems of client disconnection within a
SUBSCRIBE or PSUBSCRIBE context.

Commited changes are still experimental.
Stealing more great stuff from src/pkg/net/fd_* to watch file descriptors.
Adding a restriction for bcommand() so you can only use it in a non-blocking context.
Updating example with NonBlocking connection.
Updating example with non-blocking connection.
Updating docs. Adding a panic() when an user tries to use Subscribe() or PSubscribe() on a blocking connection.
Merge with async.
Adding tools for nice benchmarking comparison. See http://www.cnblogs.com/getong/archive/2013/04/01/2993139.html