Currently, if `--confcutdir` is not set, `inipath.parent` is used, and
if `initpath` is not set, then `confcutdir` is None, which means there
is no cutoff.
Having no cutoff is not great, it means we potentially start probing
stuff all the way up to the filesystem root directory. So let's add
another fallback, to `rootpath`, which is always something reasonable.
Ran Benita