Filelog based copy tracing only trace copy for file that have been added. This
is a trade off between skipping some rare copy case in exchange for avoiding
atrocious-to-the-point-of-unusable performance.
The changeset centric copy tracing does not need this trade off and naturally
trace all copy, include the one involving non-new files.
In order to ease the comparison from both algorithm, we add a small devel option
to trace copy for all files in the target revisions.