tests: add `hg log -G` output when there are merge conflicts The next commit will change the behavior for these. I've used slightly different commands in the different tests to match the surrounding style. Differential Revision: https://phab.mercurial-scm.org/D8042

revset: add a revset for parents in merge state This may be particularly useful soon, when I'm going to change how `hg rebase` sets its parents during conflict resolution. Differential Revision: https://phab.mercurial-scm.org/D8041