match: add tests for visitdir functionality
There are a few cases that we could have done better with some additional logic;
I tried to annotate these when I noticed them, but may have missed some. The
tests are not exhaustive; there are certainly some patterns that I didn't test
well, and many that I didn't test at all.
The primary motivation was to get coverage on visitdir so that I can cover
identical cases in a similar method I'm working on, to make sure that this new
method behaves the same (or better).
Differential Revision: https://phab.mercurial-scm.org/D4128
(binary:application/octet-stream)