merge: extract _resolvetrivial() function We would eventually like to move the resolution of modify/delete and delete/modify conflicts to the resolve phase. However, we don't want to move the checks for identical content that were added in 902554884335 (merge: before cd/dc prompt, check that changed side really changed, 2014-12-01). Let's instead move these out to a new _resolvetrivial() function that processes the actions from manifestmerge() and replaces any false cd/dc conflicts. The function will also provide a natural place for us to later add code for resolving false 'm' conflicts.