Purging commit-then-send asynchronous output

OTMA clients that support asynchronous commit-then-send message output can have OTMA purge output from a tpipe queue when the I/O PCB output cannot be delivered to the OTMA client.

To specify the purge function, the OTMA client must set the purge flag in the OTMA state data prefix of either the original input message or the NAK response when the output cannot be retrieved.