test-copies: introduce case combining the `p` and `q` branch
That case involves conflicting copies information from each branch. It is
similar to the `mAEm` / `mEAm` case except this case actual content merge is
involved too.
Differential Revision: https://phab.mercurial-scm.org/D10057
#require docutils gettext
$ $TESTDIR/check-gendoc it
checking for parse errors