stgit.el update

[nicolas-graves]

Hi StGit!

I was trying to package stgit.el for Guix, and I noticed tere is quite some cleaning to do on stgit.el, I have the following warnings on compilation: log.txt

I also wondered about the status of the package, I've seen that magit-stgit has been updated and I'm wondering if the statement

If you are looking for full fledged StGit support in Emacs, then have a look at `stgit.el' which is distributed with StGit.

as found on MELPA stable still holds true, or if magit-stgit is the one recommended now (maybe we should make a release for MELPA stable ?).