extensions: always include traceback when extension setup fails I have spent a lot of time debugging extensions that failed to load because we don't include a traceback and I didn't realize I could get traceback for the extension failure with --traceback. Let's just turn them on by default, since it should be rare that the user sees these tracebacks anyway (and if they do, it's not so bad if the extra traceback pushes them a little harder to report the problem). Since we already had a test case with --traceback and one without, I just removed the one with the flag. Differential Revision: https://phab.mercurial-scm.org/D1164