Fix problem with sync operations under very rare circumstances

This patch creates a special message queue for synchronization messages.
This prevents a situation in which messages are queued in the
new_message_queue but have not yet been originated from corrupting the
synchronization process.

Signed-off-by: Steven Dake <sdake@redhat.com>
Reviewed-by: Jan Friesse <jfriesse@redhat.com>
Reviewed-by: Fabio M. Di Nitto <fdinitto@redhat.com>