remote rename: warn when refspec was not updated

When renaming a remote, we also try to update the fetch refspec
accordingly, but only if it has the default format. For others, such
as refs/heads/master:refs/heads/origin, we are conservative and leave
it untouched. Let's give the user a warning about refspecs that are
not updated, so he can manually update the config if necessary.

Suggested-by: Jeff King <peff@peff.net>
Signed-off-by: Martin von Zweigbergk <martin.von.zweigbergk@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/remote.c

@@ -682,6 +682,12 @@ static int mv(int argc, const char **argv)
 				      ptr-buf2.buf + strlen(":refs/remotes/"),
 				      strlen(rename.old), rename.new,
 				      strlen(rename.new));
+		else
+			warning("Not updating non-default fetch respec\n"
+				"\t%s\n"
+				"\tPlease update the configuration manually if necessary.",
+				buf2.buf);
+
 		if (git_config_set_multivar(buf.buf, buf2.buf, "^$", 0))
 			return error("Could not append '%s'", buf.buf);
 	}