An initial (and quite naive) implementation was done
for conf.d/ files but features do need it as well --
which became obvious during a casual inspection of
distro/alt-workstation's target graph (which occured
broken).

The code is a messy hackery unfortunately, regexes used
are fragile regarding e.g. [A-Z_] in target names.
Read with care.

NB: lib/ might need this too but it's rather stable
    and contains some special cases that would obstruct
    the regexes even more...

The preceding commit fixes an easy but somewhat nasty bug
that spoils graphs (REPORT=1) and the fix for it spoils
merging side branches touching these files; so it's worth
a linter procedure, even if it's pretty trivial.