evolve: extract displayer to _solveone() I extracted this displayer method to _solveone() so that it would be easy to pass a different template to show evolve msgs. In upcoming patches we will be using stacktemplate in some cases where we want to include stack alias s# in evolve msgs.

utility: add a template alias that will be used in evolve msgs This template use stack alias s# instead of rev number in messages printed when we run `hg evolve`. For example, this template's msgs will look like this: move:[s3] add aaa atop:[s2] add bbb move:[s4] add ccc I will be using this template in upcoming patches.