evolve: add new variable and comment Add comment and introduce a new variable to keep track of if the progress ui is shown. Later on we will use this variable in the implementation of the --rev option.

evolve: move code to track progress and start node This makes it easier to refactor the evolve function in this serie of patches.

evolve: renaming of a variable tro was not a really descriptive name, replacing it with nexttrouble.

evolve: refactoring of the code displaying error when no trouble found Before this patch, we had many return statements in the evolve function especially in the part in charge of displaying errors when no troubles were found. We move this code in a separate function.