match: fix the rust-side bug in visit_children_set for rootfilesin matchers The fix is checked by `test_pattern_matcher_visit_children_set` test, which is what caught the bug in the first place, but also by an end-to-end test that I made for this purpose. Accept the new results of Cargo tests Many of these were already annotated with "FIXME", which is a good sign.

To run the tests, do:

cd tests/
python run-tests.py

See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.