Allow safe multi-threaded access to JedisPubSub

If Thread A calls a subscribe method on Jedis it will block on a socket read
call waiting for messages or subscription notifications.  Thread B is now free
to call additional methods on JedisPubSub to change the current subscriptions
that thread A is waiting for.  Essentially Thread A will do reads on the
socket and Thread B will do writes.

An issue occurs in that while Thread A is doing reads, in the
getObjectMultiBulkReply() method there is an implicit flush() call.  This
means both Thread A and Thread B may do a write to the socket.  Under this
situation if Thread A does a flush while Thread B is writing the internal
buffer will be corrupted.  The fix is to make thread A never call flush().
This allows Thread A to be solely reads and Thread B to be solely writes.

Additionally since Thread B is sending commands, the internal pipeline count
is incremented and never decremented.  So when Thread A terminates it's read
it resets the pipeline count.
Merge branch 'pubsub-concurrency' of github.com:ibuildthecloud/jedis into ibuildthecloud-pubsub-concurrency

Conflicts:
	src/main/java/redis/clients/jedis/Connection.java
	src/main/java/redis/clients/jedis/JedisPubSub.java