contrib: fix import-checker to operate on str instead of bytes I believe this is fallout from other Python 3 cleanups, and our code linting tools are now leaning towards operating on str and not bytes. I don't feel strongly, so I've just restored this tool to working on Python 3. Differential Revision: https://phab.mercurial-scm.org/D6453

verify: use self._err not self.err, it changed in 7eaf4b1ac2a3 Differential Revision: https://phab.mercurial-scm.org/D6451

tests: make run-tests exit non-zero if there are "errors" Previously, if there was an error such as a broken .t file that caused run-tests.py to encounter an exception during parsing, the test would be considered in an "errored" state, which is separate from "failed". The check for whether to exit non-zero or not was based entirely on whether there were any tests in a "failed" state, so if there was only an error, run-tests would exit with 0. Our test infrastructure would then consider the test as passing, causing us to have some tests with false negatives that have gone undetected for a few weeks now. Differential Revision: https://phab.mercurial-scm.org/D6452