I would like suggestions of how to rename things,  I went with `_` because it was easy.  What I really want to do is make a module `backend_*_pyplot` which contains the `Gcf` related code, but that would break badly break the API.  `backend_*_clean` seems misleading, `backend_*_stateless` seems too long, any abbreviation seems too cryptic.  Should have made clear that I don't think this is near being ready to merge.