System.sleep(uint16_t wakeUpPin, uint16_t edgeTriggerMode, long seconds) and attachInterrupt()

[RobMeades]

Hi there. It appears that if one has an interrupt attached to a pin, and then one wants to put the system to sleep and wake-up on that pin, the System.sleep() call replaces the call that you had previously attached to that interrupt.

The documentation should mention this, as it had me fooled for an entire day. I have raised a separate issue on the firmware [(https://github.com/spark/firmware/issues/1029)] as I think this behaviour is problematic. But for now at least the documentation needs a nice clear Note:.