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>> ...