Redis

* Fixed a bug in ZREVRANK where retrieving the rank of a value not in
the zset would raise an error.
* Fixed a bug in Connection.send where the errno import was getting
overwritten by a local variable.
* Fixed a bug in SLAVEOF when promoting an existing slave to a master.
* Reverted change of download URL back to redis-VERSION.tar.gz. 2.2.1's
change of this actually broke Pypi for Pip installs. Sorry!

* Changed archive name to redis-py-VERSION.tar.gz to not conflict
with the Redis server archive.

* Implemented SLAVEOF
* Implemented CONFIG as config_get and config_set
* Implemented GETBIT/SETBIT
* Implemented BRPOPLPUSH
* Implemented STRLEN
* Implemented PERSIST
* Implemented SETRANGE