update: move default destination computation to a function...
update: move default destination computation to a function
We ultimately want this to be accessible through a revset, but there is too
much complexity here for that to work. Especially we'll have to return more
than just the destination to control the behavior (eg: bookmarks to activate,
etc).
To prevent cycle, a new module is created, it will receive other
destination/behavior function in the future.
