evolve: merge commit messages while resolving content-divergence (issue5877) While resolving content-divergence, there can be divergence in commit messages too which should be resolved. This patch uses the hg's internal merge API's to merge commit messages of divergent changesets with predecessor as the base. In case of conflicts, we fallback to divergent's commit message which should be changed in future. We should pop up the editor with the commit message and the conflict markers and let user fix that. Tests are added for the functionality added.

evolve: move if-else block under the right block the index related if-else should be only executed when all three base, divergent and other have different branch names. I coded this last night and mistakenly mis-indented it. Caught when I was adding more tests.