fix a focus race condition in two ways:

fix a focus race condition in two ways:

1. when focusing a window, ignore any enter events up until the serial of the X event causing the focus, not up until the last thing sent to the server.  if we get 2 enters very quickly, then we don't want to ignore the second one just because we are focusing the first window.
2. there is a race if you check (focus_client != d->client) in the delay_focus_func, because the current focused window might change by the time this focus_client would take effect, so don't check that.