RPC ACK message format inconsistent

[jdmnd]

The RPC ACK message format is inconsistent with other types of message.

In the message specs generally, the name of an event/record/rpc is the third field of the message unless the message action is A(ACK) or E(ERROR), in which case it is the fourth field.
e.g.

R|D|recordName
R|A|D|recordName

However, RPC REQ(REQUEST) ACKs use the format P|A|rpcName|correlationId, with the rpcName in the third field. This is inconsistent with RPC S(SUBSCRIBE)/US(UNSUBSCRIBE) ACKs that have the rpcName in the fourth field: P|A|S|rpcName.

This makes the message format difficult to parse, and may lead to unspecified behaviour, ACK_TIMEOUTs or UNSOLICITED_MESSAGE errors if RPCs are named "S" or "US".