Merge branch 'configurable-socket-mgr-thread-priority' of https://github.com/mckenzieg1/StackExchange.Redis into mckenzieg1-configurable-socket-mgr-thread-priority

# Conflicts:
#	StackExchange.Redis/StackExchange/Redis/SocketManager.Poll.cs
#	StackExchange.Redis/StackExchange/Redis/SocketManager.cs