Add support for connecting to Redis via a unix domain socket and
perfer those connections over TCP connections.

lib/live_resource/redis_client.rb
	When instantiating the first Redis object, it will now attempt
	to first connect via a unix domain socket.  If it is unable to
	do so, it will fallback to a TCP connection (just like what was used
	before).

	By default, Redis is not configured to accept unix domain socket
	connections.  Plus, the socket to be used is configurable.  Thus,
	LiveResource will try a few different typical sockets, include the
	default "/tmp/redis.sock", before giving.  In the future, we
	might want to make this user-configurable, perhaps via an
	environment variable.