Please catch net.errClosing to make testsuite less noisy

When I run:
  $ go test
I get a bunch of warnings like:
2015/01/08 15:49:05 Failed to read message: read unix @/tmp/dbus-zHJNnoqO8z: use of closed network connection

The reason appears to be that the recieveLoop() is not stopped when Connection.Close() is called. One way to stop this log output is to catch the net.errClosing error. Attached is a patch that does that. Alternatively (probably better) the loop is stopped on Close().

Thanks,
 Michael