tests/test-check-execute.t

match: add visitchildrenset complement to visitdir

`visitdir(d)` lets a caller query whether the directory is part of the matcher.
It can receive a response of 'all' (yes, and all children, you can stop calling
visitdir now), False (no, and no children either), or True (yes, either
something in this directory or a child is part of the matcher).

`visitchildrenset(d)` augments that by instead of returning True, it returns a
list of items to actually investigate.  With this, code can be modified from:

    for f in self.all_items:
        if match.visitdir(self.dir + '/' + f):
            <do stuff>

to be:

    for f in self.all_items.intersect(match.visitchildrenset(self.dir)):
        <do stuff>

use of this function can provide significant performance improvements,
especially when using narrow (so that the matcher is much smaller than the stuff
we see on disk) and/or treemanifests (so that we can avoid loading manifests for
trees that aren't part of the matcher).

Differential Revision: https://phab.mercurial-scm.org/D4130

#require test-repo execbit

  $ . "$TESTDIR/helpers-testrepo.sh"
  $ cd "`dirname "$TESTDIR"`"

look for python scripts without the execute bit

  $ testrepohg files 'set:**.py and not exec() and grep(r"^#!.*?python")'
  [1]

look for python scripts with execute bit but not shebang

  $ testrepohg files 'set:**.py and exec() and not grep(r"^#!.*?python")'
  [1]

look for shell scripts with execute bit but not shebang

  $ testrepohg files 'set:**.sh and exec() and not grep(r"^#!.*(ba)?sh")'
  [1]

look for non scripts with no shebang

  $ testrepohg files 'set:exec() and not **.sh and not **.py and not grep(r"^#!")'
  [1]