Replicator should try /db/_session before /_session
Added WebSockets-Cocoa library as submodule
WIP: WebSocket-based _changes feed is basically working
WIP: WebSocket improvements. Use HTTPLogic class in SocketChangeTracker.
Implemented -changeTrackerCaughtUp
Don’t use WebSocket for _changes feed if an HTTP proxy is required

…because my WebSocket class doesn’t support proxies yet.
Require gateway version 0.91 to use WebSockets
Updated WebSockets-Cocoa submodule.