Backwards compatibility with extrainmessage broken

Created originally on Bitbucket by Felipe Contreras

When hg-git-rename-source was introduces it was added unconditionally in order to not break bidirectionality, however, that only applies if debugextrainmessage is not set.

The hg-git-rename-source change broke bidirectionality tests with git-remote-hg, the following patch restores it back.