upload-pack: prepare for sideband message support.

This does not implement sideband for propagating the status to
the downloader yet, but add code to capture the standard error
output from the pack-objects process in preparation for sending
it off to the client when the protocol extension allows us to do
so.

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

pack-objects.c

@@ -1221,6 +1221,10 @@ int main(int argc, char **argv)
 				local = 1;
 				continue;
 			}
+			if (!strcmp("--progress", arg)) {
+				progress = 1;
+				continue;
+			}
 			if (!strcmp("--incremental", arg)) {
 				incremental = 1;
 				continue;