merge: use separate lists for each action type This replaces the grand unified action list that had multiple action types as tuples in one big list. That list was iterated multiple times just to find actions of a specific type. This data model also made some code more convoluted than necessary. Instead we now store actions as a tuple of lists. Using multiple lists gives a bit of cut'n'pasted code but also enables other optimizations. This patch uses 'if True:' to preserve indentations and help reviewing. It also limits the number of conflicts with other pending patches. It can trivially be cleaned up later.