discovery: if a push would create a new head, mention the bookmark name if any

revert: use p2 as parent when reverting against it revert was always using p1 as parent. This created some minor misbehavior when reverting against p2. See test change for an example of that. This is also a useful cleanup for coming refactoring to revert.

revert: explicitly get status against the parent This makes absolutely no functional changes. The default value for node1 is already the same as the current value of parent. But to be able to properly use the second parent in merge context, we have to start to be a bit more explicit about what we compute the status against.

revert: group related data in tuple in the dispatch table The dispatch table used to be: - action if in target manifest - action if not in target manifest - make backup if in target manifest - make backup if not in target manifest We turn this into two (action, make backup) tuples. This helps both readability of the dispatch table and handling of each case. This also prepares a refactoring where the different actions we performs, whether "file is in target manifest" or not, are determined before reaching this loop.