evolve: use stack alias s# in `hg evolve` msgs As repository grows revision number lose their usefulness. To make it a little better than now, after this patch we will be using short stack aliases introduced by the topic extension (as displayed by `hg stack`). These stack aliases s# will be used only when user has enabled topic extension and his repo's current active topic is same as the revs to be evolved. For now, this patch doesn't cover `continue` case. I will discuss about this with Pierre-Yves David. Maybe we have to store the info in evolvestate that "we were using stack aliases".