Merge branch 'jc/format-patch-rfc-more'

The "--rfc" option of "git format-patch" learned to take an optional string value to be used in place of "RFC" to tweak the "[PATCH]" on the subject header. * jc/format-patch-rfc-more: format-patch: "--rfc=-(WIP)" appends to produce [PATCH (WIP)] format-patch: allow --rfc to optionally take a value, like --rfc=WIP