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.
=============================Training supports=============================Contributing============The main source for the supports is the `slides.md` but it doesn't containsall the source.The `slides.md` file contains several snippets that are replaced by otherfiles at compilation time.For example:..code::markdown ~~~raw-file output/fix-a-bug-base.log ~~~Will replace this three lines by the content of the file `output/fix-a-bug-base.log` which is generated when running the .t test file (see below forinstruction how to do that)...code::markdown ~~~graphviz-file graphs/fix-bug-1.dot ~~~Will replace this three lines by the svg rendering of the graphviz definitionin the file `graphs/fix-bug-1.dot`. This file is generated when running the .ttest file (see below for instruction how to do that).Environment preparation=======================This training supports needs pandoc to compile.You'll need a copy of the Mercurial source in order to generate the trainingsupports.You will also needs a functioning Python environment with the possibility touse `pip install` with your current user. In doubt, you can use a `virtualenv<https://virtualenv.pypa.io/en/stable/>`.You can then run the `prepare.sh` script that will configure the environmentfor you.Generating the supports=======================First, you need to run a .t test file to generate a bunch of files. You canrun the test file with this command:`python /PATH/TO/MERCURIAL/tests/run-tests.py -l test-training.t`It should have generated files in at least two directories: `graphs` and`output`.Finally, launch the `compile.sh` to generate the `index.html` output file.