chgserver: use relative path at socket.bind Before this patch, if the server address is long, the server will fail to listen and throw the error: socket.error: AF_UNIX path too long It is because AF_UNIX path usually has a very short length limit (107 chars on common platforms, see sys/un.h). This patch addresses the issue by using relative path instead. Therefore the directory length does not matter. It helps run tests with chg using a long $TMPDIR.