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.