Add -m/--modified to show files that have been modified wrt. the index.
[jc: The original came from Brian Gerst on Sep 1st but it only checked
if the paths were cache dirty without actually checking the files were
modified. I also added the usage string and a new test.]
Signed-off-by: Junio C Hamano <junkio@cox.net>
Junio C Hamano