Interesting items from ChangeLog:
o cached_realpath(): avoid hitting filesystem more than necessary.
o meta.c: refactor need_meta decision, add knobs for
missing meta file and filemon data wrt out-of-datedness.
o meta.c: missing filemon data is only relevant if we read a
meta file.
Also do not return oodate for a missing metafile if gn->path
points to .CURDIR