test: use a shorter test name This is still long but easier to read.

stack: rename troubledcount to unstablecount

evolve: use --all by default (BC) allopt defaults to None to avoid touching _checkevolveopts(). If it were True by default, that function would always act like the flag was provided by user, and so using --abort, --stop, --continue or --rev on their own would never work (hg evolve will complain that you cannot specify both --rev and --all). A notable change in tests is "no troubled changesets" line that gets printed when using `hg evolve` to update to the evolved successor of working directory parent, but there were no actual instabilities.