tests/test-gendoc-it.t

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>>
  ...

#require docutils gettext

  $ $TESTDIR/check-gendoc it
  checking for parse errors