tests: add test about handling phase-divergent merges We don't handle phase-divergent merges and we should. Upcoming patches will add the ability to handle them.

evolve: show a message when evolution leads to no changes to commit In case of orphan resolution, evolution may result in no changes to commit. This patch adds a use message in such cases. This is same as the rebase behavior.

evolve: pass the instability category to relocate() and _finalizerelocate() This patch adds category argument to relocate() and _finalizerelocate() functions to take the type of instability which we are processing so that we perform actions accordingly.