make update-index --chmod work with multiple files and --stdin
make update-index --chmod work with multiple files and --stdin

The patch makes "--chmod=-x" and "--chmod=+x" act like "--add"
and "--remove" to affect the behaviour of the command for the
rest of the path parameters, not just the following one.

Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git