Merge with stable

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 [ original upstream message ]

run-tests: allow option parser to be extended This patch moves the OptionParser population into its own function so consumers may modify the OptionParser before arguments are evaluated. This will allow consumers to add custom options, set different defaults, etc. [ original upstream message ]

run-tests: use return values instead of sys.exit [ original upstream message ]