rebase: remove sortedstate-related confusion The following rebase implementation details are frustrating: - storing a list of sorted revision numbers in a field named sortedstate - having sortedstate be a field of the rebaseruntime class - using sortedstate[-1] as opposed to a more intuitive max(self.state) to compute the latest revision in the state This commit fixes those imperfections.

rebase: replace extrafn field with _makeextrafn invocations As per Yuya's advice, we would like to slightly reduce the amount of state which is stored in rebaseruntime class. In this case, we don't need to store extrafn field, as we can produce the necessary value by calling _makeextrafn and the perf overhead is negligible.