send-pack --thin: use "thin pack" delta transfer.

The new flag loosens the usual "self containedness" requirment
of packfiles, and sends deltified representation of objects when
we know the other side has the base objects needed to unpack
them.  This would help reducing the transfer size.

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

send-pack.c

@@ -12,6 +12,7 @@ static const char *exec = "git-receive-pack";
 static int verbose = 0;
 static int send_all = 0;
 static int force_update = 0;
+static int use_thin_pack = 0;
 
 static int is_zero_sha1(const unsigned char *sha1)
 {
@@ -41,7 +42,10 @@ static void exec_rev_list(struct ref *refs)
 	int i = 0;
 
 	args[i++] = "rev-list";	/* 0 */
-	args[i++] = "--objects";	/* 1 */
+	if (use_thin_pack)	/* 1 */
+		args[i++] = "--objects-edge";
+	else
+		args[i++] = "--objects";
 	while (refs) {
 		char *buf = malloc(100);
 		if (i > 900)
@@ -361,6 +365,10 @@ int main(int argc, char **argv)
 				verbose = 1;
 				continue;
 			}
+			if (!strcmp(arg, "--thin")) {
+				use_thin_pack = 1;
+				continue;
+			}
 			usage(send_pack_usage);
 		}
 		if (!dest) {