[PATCH 1/3] Update mode-change strings in diff output.

This updates the mode change strings to be a bit more machine
friendly.  Although this might go against the spirit of
readability for human consumption, these mode bits strings are
shown only when unusual things (mode change, file creation and
deletion) happens, output normalized for machine consumption
would be permissible.

Signed-off-by: Junio C Hamano <junkio@cox.net>
Signed-off-by: Petr Baudis <pasky@ucw.cz>