graft: move rebase cleanup code next to actual rebase This is prep for refactoring the rebase logic.

shelve: add a bundlerepo method

dirstate: merge falls through to otherparent This lets us more correctly fix the state when we use setparents, as demonstrated in the change in test-graft.t.

dirstate: use 'm' state in otherparent to reduce ambiguity In rebase-like operations where we abandon the second parent, we can correctly fix up the state in setparents.

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.