dirstate: properly clean-up some more merge state on setparents

phases: move root phase assignment to it's own function This moves the initial root phase assignment to it's own function. Future patches which make phase calculations lazy will use this function to pre-fill certain phases which can be deduced from the roots.

phases: add invalidate function Phase cache invalidation was spread all over the place. Let's add a function to unify it. Later more will be added to this function.

phases: change phase command change detection A future patch is going to make phase computation lazy, so the phase command can no longer read and diff the entire phase list directly. This changes the phase command to build it's own list for diff purposes.

spanset: remove `.set()` definition All my friends are dead.

generatorset: remove `.set()` definition All my friends are dead.

addset: remove `.set()` definition All my friends are dead.

filteredset: remove `.set()` definition All my friends are dead.

baseset: remove `set()` definition All my friends are dead.

abstractsmartset: remove `set()` method definition Now that all usages have been removed, we can drop this not so useful part of the API. We can note that the name was wrong all along...

match: check if an object is a baseset using `isascending` instead of `set` The `set()` method is going away.

getset: check if an object is a baseset using `isascending` instead of `set` The `set()` method is going away.