Add a regex validator factory.
Add a __base__ class for FieldsBase (also used by RegexValidateBase) so that super() calls have a sink. This solve the problem of `object.__init__` not acceptin any arguments.
Make this 2.6 compatible.
Rename some internals to make things more clear, there are 2 (very different) kinds of factories.
Add a work-around for the lack of common metaclass issue (eg: you would use multiple field bases, with hopefully same field layout, as baseclasses to something).