This makes it possible to add paths that have funny characters (TAB
and LF) in them, and makes adding many paths more efficient in
general.

New flag "--stdin" to update-index was initially added for different
purpose, but it turns out to be a perfect match for feeding "ls-files
--others -z" output to improve "git add".

It also adds "--verbose" flag to update-index for use with "git add"
command.
Signed-off-by: NJunio C Hamano <junkio@cox.net>