Branch b1_8

Branch b1_8
Description: fix racy locking of mballoc block bitmaps causing BUG
Details    : The locking of the mballoc buddy bitmap and the in-memory
	     block bitmap was using two different spin locks in some
	     cases.  This made it possible to incorrectly access the
	     mballoc bitmap while another process was modifying it,
	     causing a sanity assertion to fail.  While no on-disk corruption
	     was reported, there was some risk of this happening.
b=18810
i=alex