Fixes issue JCBC-26 - CPU pegged with an idle connection

http://www.couchbase.com/issues/browse/JCBC-26 

The thread was sitting in a tight loop when there was nothing to do. This adds a timeout to the write queue polling method so that it waits for something to do. Increasing the timeout will further reduce looping but will increase the latency when reconfiguring a client or shutting down a view.