warn and reject reentering streams at client too

Clients now check whether their streams are attempting to re-enter
the Tor network (i.e. to send Tor traffic over Tor), and they close
them preemptively if they think exit relays will refuse them.

See bug 2667 for details. Resolves ticket 40271.
9 jobs for ticket40271_046_01 in 19 minutes and 4 seconds (queued for 9 minutes and 10 seconds)