phase: add a passing test for (issue3575) Apparently this issue was fixed along the way (If it ever existed at all…)

run-tests: allow test paths in other directories Previously, test paths were assumed to be in the same directory and wouldn't have a directory component. If a path with a directory component was specified, it would be filtered out. This change allow paths to contain directories. This in turn allows tests from other directories to be executed. Executing tests in other directories may break assumptions elsewhere in the testing code. However, on initial glance, things appear to "just work." This approach of running tests from other directories is successfully being used at https://hg.mozilla.org/hgcustom/version-control-tools/file/7085790ff3af/run-mercurial-tests.py