merge: separate out "both created" cases When 'f' is not in 'ma', 'a' will be 'nullid' and all the if/elif conditions that check whether some one nodeid is equal to 'a' will fail, and the else-clause will instead apply. We can make that more explicit by creating a separate 'm' action for the case where 'a' is 'nullid'. While it does mean copying some code, perhaps it makes it a little clearer which codepaths are possible, and which cases the "Note:" in the code refers to. It also lets us make the debug action messages a little more specific.