We'll try to avoid calling Cwd::abs_path and use
File::Spec->rel2abs instead, since abs_path will resolve
symlinks the user specified on the command-line.
Unfortunately, ->rel2abs still leaves "/.." and "/../"
uncollapsed, so we still need to fall back to Cwd::abs_path in
those cases.
While we are at it, we'll also resolve inboxdir from deep inside
v2 directories instead of misdetecting them as v1 bare git
repos.
In any case, stop matching directories by name and instead rely
on the unique combination of st_dev + st_ino on stat() as we
started doing in the extindex code.