circuit_t into origin_circuit_t and or_circuit_t.  I fixed some
segaults; there may be more.  We still need to move more rendezvous
stuff into subtypes.

This is a trial run for splitting up connection_t; if the approach is
insane, please say so soon so we can do something smarter.

Also, this discards the old HALF_OPEN code, which nobody seems to
want.


svn:r6817