New 'DisableNetwork' option to prevent Tor from using the network
Some controllers want this so they can mess with Tor's configuration for a while via the control port before actually letting Tor out of the house. We do this with a new DisableNetwork option, that prevents Tor from making any outbound connections or binding any non-control listeners. Additionally, it shuts down the same functionality as shuts down when we are hibernating, plus the code that launches directory downloads. To make sure I didn't miss anything, I added a clause straight to connection_connect, so that we won't even try to open an outbound socket when the network is disabled. In my testing, I made this an assert, but since I probably missed something, I've turned it into a BUG warning for testing.