Clients should alert the user if many guards are unreachable

If the user is behind a restrictive firewall, in a censored location, or is otherwise restricted in the number of guards they can use, the Tor Client should inform them of this fact.

Depending upon the rate of guard failure, tor should emit either a notice or a warn.

We should probably also perform a quick check to see if all guards are on a small subset of non-default ports, or perhaps just 80 or 443.