Revert option for git add --patch

Hi,

I would like to propose a revert option for 'git add --patch', that reverts the hunk. I often use `git add -p` to skip whitespace changes when preparing a patch, and a 'revert' option would save me from running 'git checkout <file>' after I've staged the desired changes.

I would propose adding r and R options for the 'Stage this hunk' menu, with the following actions:

r: Revert this hunk
R: Revert this hunk and all other remaining hunks

e.g. Stage this hunk [y/n/a/d/K/j/J/e/r/R?]?

Please let me know if you think this is a good idea.

Best, Nathan