Add NULL message sending to the bench mark
Add NULL message sending to the bench mark

To see how long it takes to send nothing. This is mostly to verify that
my current strategy for idle time counting is correct in assuming that
it will take at least 3 microseconds to get from a hardware interrupt
back to the idle task (in the fastest case).
ferrous26/cs452-flaming-meme,ferrous26/cs452-flaming-meme,ferrous26/cs452-flaming-meme