Fix for BUG#11704: "Found locks from different thread" warnings:
 The source of warnings was this scenario in OPTIMIZE:

     thr1: lock table with TL_WRITE_ONLY (InnoDB converts lock to
     TL_WRITE_ALLOW_WRITE)

     thr2: (UPDATE command) obtains a TL_WRITE_ALLOW_WRITE lock

     thr1: call mysql_lock_abort(). This function sets type of thr'1 lock
     to TL_WRITE_ONLY

     thr2: try to release thr2's lock. See two locks: TL_WRITE_ONLY,
     TL_WRITE_ALLOW_WRITE and produce a warning.
   
The fix: Make InnoDB not to convert TL_WRITE_ONLY locks to
TL_WRITE_ALLOW_WRITE in OPTIMIZE TABLE.