High: AIS: Messaging fixes and enhancements

• Only add the async channel to mainloop
• Switch to saSendReceiveReply() which expects an ACK on the sync channel when the peer got the message
• Support busy peers which request a resend of the message
• mar_res_header_t header instead of mar_req_header_t header in AIS_Message
• Recieve only mar_res_header_t as the header (in order to decide how big the payload is) and obtain the rest of AIS_Message (including .data) as the payload
• Better logging of transitional membership events

Mercurial revision: a26a90507113554b57fdf227df5f3a558dc6b28f