MFC r175055

MFC r175055
  Defer setting either PG_CACHED or PG_FREE until after the free page
  queues lock is acquired.  Otherwise, the state of a reservation's
  pages' flags and its population count can be inconsistent.  That could
  result in a page being freed twice.

(This change should have been included in the MFC of the superpages
support.)

Thanks to:	pho for an illuminating crash

Approved by:	re (kib)

git-svn-id: svn://svn.freebsd.org/base/releng/7.2@191209 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f