Update git-diff-script.

Update git-diff-script.

This uses the fixed rev-parse to allow passing diff options to the
underlying diff command.  For example:

    $ git diff -r HEAD

shows the output in raw-diff format, and

    $ git diff -p -R HEAD | git apply

generates a patch to go back from your working tree to HEAD commit
(i.e. an expensive way to say "git checkout -f HEAD").

At the same time, it accidentally removes the use of shell arrays.

Signed-off-by: Junio C Hamano <junkio@cox.net>