Major mode for viewing/editing context diffs.
Supports unified and context diffs as well as (to a lesser extent)
When the buffer is read-only, the ESC prefix is not necessary.
If you edit the buffer manually, diff-mode will try to update the hunk
headers for you on-the-fly.
You can also switch between context diff and unified diff with M-x diff-context->unified,
or vice versa with M-x diff-unified->context and you can also reverse the direction of
a diff with M-x diff-reverse-direction.
Uses keymap `diff-mode-map', which is not currently defined. (fn)