sendACK() restting SENDERID to 0

[jkittley]

It looks like the while not self.canSend() loop in sendACK() is resetting all the SENDERID and RSSI values in the class. The reason why is perfectly understandable, however if the sendACK() occurs before the end of the loop i.e. you try to use SENDERID after sending the Acknowledgement this is a bit confusing. Maybe it would be better to have receiveDone() return values so that they are separated? Or just add a comment for idiots like me.