evolve: add logic to decide local and other side before merge Before we perform merge between the two content-divergent csets, this logic decides which cset would reside at which side i.e. local or other. for e.g. in case of public content divergence where one side of divergence is public, we always keep public one to local side. (this logic of always keeping public one to local side may change in future, but for now that's what it is.)