1.0.4.17: interrupt handler spring cleaning

1.0.4.17: interrupt handler spring cleaning

 * interrupt_handle_now was always called with the real context, not
   a void context: remove the useless cast. Also fix
   FOREIGN_FUNCTION_CALL_FLAG usage there.

 * low_level_interrupt_handle_now was also always called with the real
   context, not a void context: useless cast is now gone. It also
   needs no FP control restoration or Darwin context fixage.

 * maybe_now_maybe_later and low_level_maybe_now_maybe_later were
   missing the Darwin context fix on one codepath.

 * interrupt_handle_now_handler was missing the FP control fixage.