- Allocate mounts from a uma zone that uses UMA_ZONE_NOFREE to prevent

 - Allocate mounts from a uma zone that uses UMA_ZONE_NOFREE to prevent
   mount memory from being reclaimed.  This resolves a number of race
   conditions described in vfs_default.c and introduced with the
   VFS_LOCK_GIANT macros.
 - Let the mtx and lock remain valid after the mount structure has been
   freed by using init and fini calls.  Technically fini will never be
   called but is included for completeness.
 - Consistently use lockmgr directly rather than lockmgr to lock and
   vfs_unbusy to unlock.

Discussed with:	tegge
Tested by:	kris
Sponsored by:	Isilon Systems, Inc.