Cleanup some of the PVR code

I've started looking at the PVR subsystem to get a grip on how it works so I can eventually fix some bugs in the future. The changes here were done as a part of that process (and as Linux gitfu training since I've been spoiled by SourceTree on Windows).

The only possible functionality change is the addition of a missing lock in IsConnectedClient(). All other methods that loop on the client map uses a lock so I figured it should be here too.