match: explode if unsupported pattern passed down to _regex() builder

match: add basic wrapper for boolean function This serves as a generic wrapper for fileset predicates. In future patches, a fileset expression will be mapped to a tree of matchers for a better support of match attributes such as visitdir(). For example, $ hg debugwalk -v 'set:contrib/** and binary()' * matcher: <intersectionmatcher m1=<patternmatcher patterns='(?:contrib/.*$)'>, m2=<predicatematcher pred=binary>> ...

stringutil: move _formatsetrepr() from smartset I'll add a matcher subclass wrapping a boolean function, which will use buildrepr() to provide debugging information in a similar way to smartset.filteredset.