sim_cycle_timers: reworked process timer function and modified insertion routine.

added avr_cycle_timer_insert_at_when, taking next cycle as whole
 instead of as offset.
avr_cycle_timer_insert is now a wrapper funciton passing
 when + avr->cycle to insert_at_when.
process_timer now calls insert_at_when eliminating double work of
 subtracting avr->cycle from when only to have timer_insert adding
 it back.

	modified:   sim/sim_cycle_timers.c