Use last event time when calling XSetInputFocus

[rbernon]

This fixes a race condition when WM_TAKE_FOCUS message is sent to client windows, with the last event time as time parameter. The client might react to the WM_TAKE_FOCUS message with a XSetInputFocus call, and is expected to pass the message time as time parameter.

As fvwm concurrently calls XSetInputFocus with CurrentTime, it causes a race condition and sometimes the X server gives focus to fvwm window, stealing the focus from the client window.