Before, there were two problems:
* Even if a pulsein was never constructed, supervisor_disable_tick
would occur during restart. This could cancel out a supervisor_enable_tick
from someplace else, with unexpected results.
* If two or more pulseins were constructed, each one would enable ticks,
but only the last one deinited (or the reset routine) would disable,
leaving ticks running indefinitely.
In my testing, it seemed that this led to the board sometimes stopping when
it should have auto-reloaded.
