Refuse connection requests to private OR addresses unless
ExtendAllowPrivateAddresses is set. Previously, tor would
connect, then refuse to send any cells to a private address.

Fixes bugs 17674 and 8976; bugfix on b7c172c9 (28 Aug 2012)
Original bug 6710, released in 0.2.3.21-rc and an 0.2.2 maint
release.

Patch by "teor".