XCU ERN 14 (diff -u)

[Paul Eggert <yyyyyy@xxxxxxxxxxx>]

I'd like to volunteer to help resolve XCU ERN 14 (diff) by drafting
text to specify the behavior of "diff -u" as supported by GNU diff
(which I maintain) along with other diff implementations.  As I
understand it you don't need the actual text right away but I can
commit to having it ready by July 31, the cutoff date.

I don't plan to make any of the other diff formats obsolete or
deprecated, as suggested in XCU ERN 14's action.