tests: support passing testcase after .t paths that have path separators This probably could have been implemented by changing the regex above this bit of code, but I wasn't sure if it would end up handling various OSes correctly, so I decided to go with this version instead. Previously: $ tests/run-tests.py tests/test-ssh.t -l running 2 tests using 2 parallel processes .. # Ran 2 tests, 0 skipped, 0 failed. $ tests/run-tests.py tests/test-ssh.t#sshv1 -l running 0 tests using 0 parallel processes # Ran 0 tests, 0 skipped, 0 failed. Now: $ tests/run-tests.py tests/test-ssh.t -l running 2 tests using 2 parallel processes .. # Ran 2 tests, 0 skipped, 0 failed. $ tests/run-tests.py tests/test-ssh.t#sshv1 -l running 1 tests using 1 parallel processes . # Ran 1 tests, 0 skipped, 0 failed. Differential Revision: https://phab.mercurial-scm.org/D5535