Have `reject *` as the default exit policy

Quoting arma in a discussion on tor-relays:

On Thu, Oct 31, 2013 at 06:12:47PM -0700, Andy Isaacson wrote:

That's correct, it takes a deliberate action on the part of the administrator to become a relay; and another deliberate action to become an exit relay.

Actually, that second part isn't true. Once you decide to become a relay, the default is to exit to most popular ports.

The main reason for this choice is the number of people who've told us that they are only able to run exit relays because "it's what Tor does when you run a relay", and their institution wouldn't let them do it if it required a manual config change to become an exit.

Then again, that was a long time ago, and maybe it's gotten harder to sustain exits these days?

I think the change is actually worth making as I have seen two users being surprised by the current default behaviour. People running an exit while not fully aware of what it means usually turn unhappy.

(In any cases, we can discuss and wontfix if the previous rationale still hold.)