check-code: move fixing up regexp into main procedure
This patch makes an extra check pattern to be prepared by
"_preparepats()" as similarly as existing patterns, if it is added to
"checks" array before invocation of "main()" in check-code.py.
This is a part of preparation for adding check-code.py extra checks by
another python script in subsequent patch.
This is also useful for SkeletonExtensionPlan.
https://www.mercurial-scm.org/wiki/SkeletonExtensionPlan
Issue351: mq: qrefresh can create extra revlog entry
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ hg qinit
$ echo b > b
$ hg ci -A -m foo
adding b
$ echo cc > b
$ hg qnew -f foo.diff
$ echo b > b
$ hg qrefresh
$ hg debugindex b
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 3 ..... 0 1e88685f5dde 000000000000 000000000000 (re)