Another try to add support to the ignore mechanism that lets you
say "this is excluded" and then later say "oh, no, this part (that
is a subset of the previous part) is not excluded".
* nd/exclusion-regression-fix:
dir.c: don't exclude whole dir prematurely
dir.c: support marking some patterns already matched
dir.c: support tracing exclude
dir.c: fix match_pathname()