ZFS_ENTER was embarrassingly still using old z_unmount_lock, which is not
even initialised. Deleted from struct, and now uses correct z_teardown_lock.

Fixed SPOTLIGHT_GET_MOUNT_TIME defines that no longer give correct value on
10.8. Will need testing on 10.6. ioctl for it used copyout which return
failure. Following hfs_vnops, we now return the data the same way.

do_unmount changed to ZOL system style, to call diskutil to unmount. Now
we can handle spotlight being on again.

mmap/pagein/pageout correctly use z_map_lock again.

Removed grow_blocksize of power-of-2 fix, as update_pages now uses
uio_duplicate() to correctly traverse the pages.