After some discussion with Fernando it was decided that detecting calls
on all magics as in pull request #352 was probably overkill. Opted for
detecting with a regex possible calls to absent Quitter objects and
rewriting them (as before), with visual notification of this rewrite.
This is done with a QuitterChecker which has priority just below that
The only case where you will get a NameError now is if you input
newlines before the starting and closing paren, but that's sufficiently
crazy as to not be worth considering (it takes one, optional,
integer argument in the real Python shell, why you'd ever need
Also subclassed MagicHandler to avoid doing the regex check twice (once
in the Checker and once in the Handler) and factored out the creation of
the replacement command so as to avoid potential code rot.