Address a race condition that was introduced in r238212.  Unless the page queues lock is acquired before the page lock is released, there is no guarantee that the page will still be in that same page queue when vm_page_requeue() is called.
Address a race condition that was introduced in r238212.  Unless the page
queues lock is acquired before the page lock is released, there is no
guarantee that the page will still be in that same page queue when
vm_page_requeue() is called.

Reported by:		pho
In collaboration with:	kib
MFC after:	3 days

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase