tests/test-gendoc-sv.t

copies-rust: make the comparison aware of the revision being current merged

This make no significant performance change in practice (all ±2%) in practice,
but it will help us to distinct between some semantically different cases later
on.

Differential Revision: https://phab.mercurial-scm.org/D9498

#require docutils gettext

  $ $TESTDIR/check-gendoc sv
  checking for parse errors