extensions: fix up many many debug logs that use %r This gets us a bunch closer on Python 3, but I'll still have to use a ton of sad globs. A previous version of this patch tried to preserve the %r formatting, but upon review Yuya noted that special characters in extension names is very unlikely, so we can just use %s and not sweat the quoting. Differential Revision: https://phab.mercurial-scm.org/D5002