mq: use exact matching in the second dirstate walking for efficiency of 'qnew' 'hg qnew' with pattern/-I/-X creates matching object with them, and uses it twice for 'dirstate.walk()': via 'repo.status()' and 'repo.commit()'. this may cause full manifest scan in the second 'dirstate.walk()', even though mq already knows complete target filenames at the first 'dirstate.walk()'. this patch creates exact matching object also in this case, and use it at 'repo.commit()' invocation to avoid full manifest scan in the second 'dirstate.walk()'. even though 'inclsubs' is added to 'pats' for original matching object, it is also passed to exact matching object, because subrepositories are deleted from result of 'dirstate.walk()' at the end of it.