Two modifications:
1. The addition of 2013 to the copyright year range for every file;
2. The use of a single year range, instead of potentially multiple
year ranges, as approved by the FSF.
* sim-events.c (sim_events_remain_time): New function returning
the time that remains before the event is raised.
* hw-events.c (hw_event_remain_time): Likewise.
* sim-events.h (sim_events_remain_time): Declare.
* hw-events.h (hw_event_remain_time): Declare.
