Add profiler for the IncrementSet class.
Improve IncrementedSet implementation.

Uses Redis server for storage now.
Much better performance -- asynchronous and 145x speedup (for 10,000 items).
Allow Redis to connect through a Unix socket.
Add config option for Redis password.
Allow Redis connection config to be passed to IncrementedSet constructor.
Add test to check for IncrementedSet emptiness.
IncrementedSet.insert() should replace existing keys.
Allow use of Redis database other than first (0).