diff: add --inverse option Most of the time, one can reverse a diff by swapping the revisions passed with -r but it happens that if you use the global -R, and diff against the tip of the current repo, you can't swap the revisions. One use-case for that is reviewing changes from a bundle before unbundling. One could also pipe the output of `hg diff` to a command line filter that reverses the diff, but that would remove the benefit from color diffs. Therefore, having an option in `hg diff` to reverse a diff is a good thing. The option flag selection was tricky. GNU patch uses -R/--reverse but -R is already used as a global option and --reverse would make --rev ambiguous.