evolve: use cmdrewrite.amend() instead of creating a new commit This patch backs out changeset 88601e1cd5d8. We replaced cmdrewrite.amend() with creating new commit because using amend(), a high level function was not good and creating a new commit gave us more control over things. **HOWEVER** to get more control, you need to get arrange all the pieces together perfectly. Creating a new commit, the existing logic has some bugs around dirstate handling, the `repo.dirstate.setparents()` call especially. Sometimes this fixes the dirstate correctly sometimes not. As Pierre-Yves David said, "Having a "clumsy" implementation with the right behavior is usually a good first step. So having an amend based implementation seems like a good first step.", let's take a step back and get back using amend so that we can have a correct basic implementation which is bug free.