Use improved credits estimates for quota operations.  Also reserve space
for a quota operation in a transaction only if filesystem was mounted with
some quota option.
Signed-off-by: NJan Kara <jack@suse.cz>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>