stack: fix printing order in case of unstability The stack was displayed using revision number order, this give good result in the simple case (straight stack) but give bad result when the stack is not linear because of unstability. We fixes it by reusing the evolution logic for sorting. As we do not live next to evolution yet, we duplicated this logic for now.

stack: exclude obsolete changeset from the set We care about relevant changeset, obsolete have a new version somewhere and we don't care about the old one in our display. In case of unstability, the ordering used is still wrong.