From: Jan Kara <jack@ucw.cz>

Change locking rules in quota code to fix lock ordering especially wrt
journal lock.  Also some unnecessary spinlocking is removed.  The locking
changes are mainly: dqptr_sem, dqio_sem are acquired only when transaction is
already started, dqonoff_sem before a transaction is started.  This change
requires some callbacks to ext3 (also implemented in this patch) to start
transaction before the locks are acquired.