Previously, when vm_page_free_toq() was performed on a page belonging to

Previously, when vm_page_free_toq() was performed on a page belonging to
a reservation, unless all of the reservation's pages were free, the
reservation was moved to the head of the partially-populated reservations
queue, where it would be the next reservation to be broken in case the
free page queues were emptied.  Now, instead, I am moving it to the tail.
Very likely this reservation is in the process of being freed in its
entirety, so placing it at the tail of the queue makes it more likely that
the underlying physical memory will be returned to the free page queues as
one contiguous chunk.  If a reservation must be broken, it will, instead,
be the longest unchanged reservation, which is arguably the reservation
that is least likely to ever achieve promotion or be freed in its entirety.

MFC after:	6 weeks