evolve: cover the orphanmerge part missed by lastsolved Let's cover the orphanmerge part also as it was missed at the time when we introduced "lastsolved". Chagnes in test-evolve.t reflect the fixed behaviour.

evolve: add test which shows orphan-merge resolution can result to crash It happens when there are still some revisions to evolve after evoluiton of a orphan-merge. And the reason behind crash is that `lastsolved` is not being updated and contain a wrong value which is now hidden. Next patch will fix this problem.