patch.difffeatureopts: add a feature for whitespace diffopts These aren't exactly format-breaking features -- just ones for which patches applied to a repo will produce incorrect commits, In any case, some commands like record and annotate only care about this feature.

patch.difffeatureopts: add a feature for diff.git This deserves to be its own feature -- indeed, this is often the only feature several commands care about.

patch: rename diffopts to diffallopts This is meant to be used when all features are explicitly requested. diffopts is kept as an alias for now -- it will go away soon.