Automatic Revert (similar to GitHub)

[BhaaLseN]

GitHub Pull Requests provide a "Revert" button at the end that create another Pull Request that does the inverse. It would probably be nice to provide a link with the issue comment that does this (or rather, shows a HTML form requiring additional confirmation before the revert is attempted). May supersede #2, but may also take longer to implement (especially with failure cases).

This should also add another issue comment with infos about how to get the changes merged correctly. https://www.kernel.org/pub/software/scm/git/docs/howto/revert-a-faulty-merge.html describes why this is the case; and why a simple additional merge won't work.