copies: make _backwardrenames() filter out copies by destination
As shown by the test case, _backwardrenames() doesn't filter by the
matcher. It doesn't show up in `hg status --copies` because that only
prints files changed between the two commits. I wouldn't be surprised
if some other command that replies on pathcopies() was broken before
this patch, but I haven't bothered to check other commands.
Differential Revision: https://phab.mercurial-scm.org/D5988
.. Common link and substitution definitions.
.. |hg(1)| replace:: **hg**\ (1)
.. _hg(1): hg.1.html
.. |hgrc(5)| replace:: **hgrc**\ (5)
.. _hgrc(5): hgrc.5.html
.. |hgignore(5)| replace:: **hgignore**\ (5)
.. _hgignore(5): hgignore.5.html