Tk_GetUserInactiveTime returns the number of milliseconds
that have passed since the last user interaction (usually via
keyboard or mouse) with the respective display. On systems and
displays that do not support querying the user inactiviy time,
-1 is returned. Tk_GetUserInactiveTime resets the
user inactivity timer of the given display to zero. On windowing
systems that do not support multiple displays display can be
passed as NULL.