Fixup a past commit and rebase autosquash

Ability, when committing changes, to fixup a past commit (if there are no merge conflcts for subsequent commits)

Suppose I have committed 

A > B > C 

..in that order. I realize I missed something on commit B, if I want to fix it I have to introduce a new Commit D, and make an interactive rebase to move commit D so it becomes A > B > D > C and merge commit B and D (we often refer to part of this process as a fixup)

I suggest improvements to the smartgit interface to be able to perform this automatically. Note that this procedure is now facilitated by the --fixup param when committing as explained here

Idea : in the commit window, we already have a "select" menu that can help copy previous messages. Introduce a similar "fixup" select menu, which allows selecting a commit similarly to "select", but when a previous commit is selected this way, transform the "commit" button so it becomes a "fixup" button and actually performs

git commit --fixup=[selected commit ref] # Commit indicating a fixup
git rebase -i --autosquash [selected-commit-ref]~1 # merge fixup commit into broken commit

(ans similarly for the other button "fixup and (force) push"

References

https://stackoverflow.com/questions/3103589/how-can-i-easily-fixup-a-past-commit