homepage

Since this has been reported already several times (see e.g. #11947), and it's a fairly common mistake, I think we should do something to avoid it.
A few possibilities are:
 1) add a warning in the doc;
 2) make count and flag keyword-only argument (raising a deprecation warning in 3.3 and actually change it later);
 3) change the regex flags to some object that can be distinguished from ints and raise an error when a flag is passed to count;