match: let regex match function return a boolean
Match function for regex pattern kind is built through
_buildregexmatch() and _buildmatch() using _rematcher() that returns a
re.match function, which either returns a match object or None. This
does not conform to Mercurial's matcher interface for call() or
exact(), which are expected to return a boolean value. We fix this by
building a lambda around _rematcher() in _buildregexmatch().
Accordingly, we update doctest examples to remove bool() calls that are