[PATCH] Add git-external-diff-script

[PATCH] Add git-external-diff-script

This is a demonstration of GIT_EXTERNAL_DIFF mechanism, and a
testbed for tweaking and enhancing what the built-in diff should
do.  This script is designed to output exactly the same output
as what the built-in diff driver produces when used as the
GIT_EXTERNAL_DIFF command.

I've run this and updated built-in diff on the entire history of
linux-2.6 git repository, and JG's udev.git repository which has
interesting symlink cases to make sure it is equivalent to the
built-in diff driver.

Signed-off-by: Junio C Hamano <junkio@cox.net>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>