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.

evolve: move logic to complete interrupted relocation to new fn This moves logic which completed the interrupted relocation to it's own separate function as we will need that function in continuing phase-divergence and content-divergence too.

evolve: move logic to complete interrupted orphan resolution to new fn This patch moves logic which completes an interrupted orphan resolution to it's own new function. We will defining such functions for completing phase-divergence and content-divergence too.