Merge branch 'ds/format-patch-rfc-and-k'

The "-k" and "--rfc" options of "format-patch" will now error out when used together, as one tells us not to add anything to the title of the commit, and the other one tells us to add "RFC" in addition to "PATCH". * ds/format-patch-rfc-and-k: format-patch: ensure that --rfc and -k are mutually exclusive