o Minor bugfixes:
    - Set the correct day of year value when the system's localtime(_r)
      or gmtime(_r) functions fail to set struct tm.
      Fixes bug 13476.
    - Avoid unlikely signed integer overflow in tor_timegm on systems with
      32-bit time_t.
      Fixes bug 13476.
  o Minor enhancements (validation):
    - Check all date/time values passed to tor_timegm and parse_rfc1123_time
      for validity, taking leap years into account.
      Improves HTTP header validation.
      Implemented with bug 13476.
    - Clamp year values returned by system localtime(_r) and gmtime(_r)
      to year 1. This ensures tor can read any values it might write out.
      Fixes bug 13476.