Merge branch 'maint-0.3.0' into maint-0.3.1

  o Major bugfixes (Exit nodes):

    - Fix an issue causing high-bandwidth exit nodes to fail a majority

      or all of their DNS requests, making them basically unsuitable for

      regular usage in Tor circuits. The problem is related to

      libevent's DNS handling, but we can work around it in Tor. Fixes

      bugs 21394 and 18580; bugfix on 0.1.2.2-alpha which introduced

      eventdns. Credit goes to Dhalgren for identifying and finding a

      workaround to this bug and to gamambel, arthuredelstein and

      arma in helping to track it down and analyze it.

#define SET(k,v)  evdns_base_set_option(the_evdns_base, (k), (v))

  // If we only have one nameserver, it does not make sense to back off

  // from it for a timeout. Unfortunately, the value for max-timeouts is

  // currently clamped by libevent to 255, but it does not hurt to set

  // it higher in case libevent gets a patch for this.

  // Reducing attempts in the case of just one name server too, because

  // it is very likely to be a local one where a network connectivity

  // issue should not cause an attempt to fail.

  if (evdns_base_count_nameservers(the_evdns_base) == 1) {

    SET("max-timeouts:", "16");

    SET("timeout:", "10");

    SET("max-timeouts:", "1000000");

    SET("attempts:", "1");

  } else {

    SET("max-timeouts:", "3");

    SET("timeout:", "5");

  }

  // Elongate the queue of maximum inflight dns requests, so if a bunch

  // time out at the resolver (happens commonly with unbound) we won't

  // stall every other DNS request. This potentially means some wasted

  // CPU as there's a walk over a linear queue involved, but this is a

  // much better tradeoff compared to just failing DNS requests because

  // of a full queue.

  SET("max-inflight:", "8192");

  // Time out after 5 seconds if no reply.

  SET("timeout:", "5");

  if (options->ServerDNSRandomizeCase)

    SET("randomize-case:", "1");

  else