/dev/power.
XXX - due to the way interrupt handling is structured we have no easy
way to defer clearing the button interrupt until the sysmon callback
has happened and the event is dispatched. We clear it imediately on
return from the interrupt handler. This means we get an interrupt storm
until the button is released, and then start to handle it.
This needs to be fixed! (But with the default application for the power
button does not make a user visible difference.)