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.

tests: add more tests for solving phase-divergence using `hg evolve` This patch adds more tests for resolving phase-divergence caused due to fold or split using `hg evolve` command. The resolution in case of split is not very good and will be fixed in upcoming patches

evolve: handle interrupted phase-divergence resolution gracefully This patch adds logic to handle the interrupted phase-divergence resolution by `hg evolve` command gracefully. We first complete the relocation of the changeset and then do the divergence resolution. Previous functions moved required code separate fucntions so that we can use them here.

evolve: move logic to resolve phase-divergence in a new function This patch moves logic which does the revert and create a commit on top of public changeset because we need to repeat that logic while handling continuation of `hg evolve` when there are conflicts while rebasing the phase-divergent changeset.

evolve: store the precursor of phase-divergent in evolvestate This patch makes `hg evolve` store the precursor of phase-divergent changeset in evolvestate so that we don't need to calculate that again.