Regular expression matcher in message filter

The regular expression matcher in message filters might not be very useful for an ordinary user, but I find it very useful to write more complicated filters and I believe it will be for many power users.

It would be really nice if two matchers are added:

* 'matches regular expression'
* 'does not match regular expression'

I would prefer the PERL or Java regular expression because it's most flexible and powerful although I can live with the well documented similar regex engine.