ACK_TIMER corner cases

[sblair]

Scott, I didn't know QUEUED_MESSAGE was optional for the controller; thanks. I do try to handle both responder ACK_TIMER implementations anyway (http://www.rdmprotocol.org/forums/showthread.php?t=731) and RDM's lack of (TFTP/HTTP-style) sequence recovery.

As I said, my belief is that everyone SHOULD use QUEUED_MESSAGES, however it is not strictly required for the controller to implement them. Of course it will be a far better controller that DOES implement them. Either way, it doesn't mean the controller can't just wait for the ACK_TIMER to expire and send the PID request again and *hopefully* the responder will have it available immediately to provide at that point.