dirs: remove mutable string optimization at all As far as I can see, the optimization trick has been dead since 42e89b87ca79 "dirs: speed up by storing number of direct children per dir". After 42e89b87ca79, the key variable is cleared to NULL at each iteration.

py3: prevent comparison with None in curses histedit (issue6196)

fix: match patterns relative to root I was surprised fixer patterns (used to determine which fixers to run) are applies to the parent directory, not the repo root directory. Danny Hooper (the author of the extension) seemed to agree that it's better to apply them to the repo root, so that's what this patch does. Differential Revision: https://phab.mercurial-scm.org/D7101

tests: add test showing that fixer patterns are currently relative to $PWD Differential Revision: https://phab.mercurial-scm.org/D7100