HSes could join a client's rend circ before the INTRODUCE_ACK arrives
A race condition could trigger the following warning message in
rend_client_receive_rendezvous if a hidden service ever joins to a client's rendezvous circuit before the client receives an INTRODUCE_ACK from the introduction-point relay:
log_warn(LD_PROTOCOL,"Got rendezvous2 cell from hidden service, but not " "expecting it. Closing.");
(This would also slow down or break the HS connection establishment process.)
This bug could be in 0.2.1.x, although we probably don't want to fix it there.
(Moved from #4759 (moved) comment 2.)