run-tests: fix Python 3 incompatibilities At one point run-tests.py and test-run-tests.t worked and passed under Python 3.5. Various changes to run-tests.py over the past several months appear to have broken Python 3.5 compatibility. This patch implements various fixes (all related to str/bytes type coercion) to make run-tests.py and test-run-tests.t mostly work again. There are still a few failures in test-run-tests.t due to issues importing mercurial.* modules. But at least run-tests.py seems to work under 3.5 again.