evolve: introduce a resolutionparent variable and store it in evolvestate This patch introduces a resolutionparent variable which will be the parent of final changeset after resolving content-divergent changesets. Till now, the parent is always the parent of one of the divergent node, but now in upcoming cases, it can be a successor of both the parents of divergent nodes.

evolve: introduce a dirstatedance() fn to fix dirstate after parent change This patch introduces a dirstatedance() function which will be used after fixing the dirstate when we change parents using repo.dirstate.setparents(). Look at docs added for more details.