MQ_PTR
MQ_PTR(mqhp, currentp)->msg_next = 0;
MQ_PTR(mqhp, currentp)->msg_next = nextp;
MQ_PTR(mqhp, nextp)->msg_next = 0;
curbuf = MQ_PTR(mqhp, currentp);
curbuf = MQ_PTR(mqhp, currentp);
MQ_PTR(mqhp, *tailpp)->msg_next = currentp;