Even if "foo" and/or "bar" does not exist in index, "git diff foo bar"
should not change behaviour drastically from "git diff foo bar baz" or
"git diff foo". A feature that "sometimes works and is handy" is an
unreliable cute hack.
"git diff foo bar" outside a git repository continues to work as a more
colourful alternative to "diff -u" as before.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
