Merge branch 'hotfix-4.4.4'
Allow multiple consumers, protect from cleanup via rwlock.

With multiple distributor threads, we were seeing high CPU usage
when the storage queue was empty because thread 0 would block waiting for
a worker and then other threads would fail to acquire the lock and just
spin until another thread got a chance to block on the Receive.
Merge branch 'cpu-fix' of https://github.com/jlewallen/NServiceBus.Distributor.Msmq into jlewallen-cpu-fix
Merge branch 'jlewallen-cpu-fix' into release-5.0.0