[PATCH] Give show-files the ability to process exclusion pattern.

[PATCH] Give show-files the ability to process exclusion pattern.

This can be used with the famous dontdiff file as follows to find out
about uncommitted files just like dontdiff is used with the diff
command:

    show-files --others --exclude-from=dontdiff

and the exclude list can be reversed with the --ignore switch.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>