Fix TImezone handling when localtime is in UTC

Fun quirk: travis CI runs UTC on their servers, so it caught this bug in
ruby 1.9.3 and up. If the localtime is in UTC, we don't need a daylight
savings offset, so the values should be correct in both UTC and offset
zones

  verified with
   * TZ="America/Chicago" rake spec
   * TZ=UTC rake spec