validate_pluggable_transports_config() is not called after SIGHUP

  /** 11c. validate pluggable transports configuration if we need to */
  if (!has_validated_pt &&
      (options->Bridges || options->ClientTransportPlugin)) {
    if (validate_pluggable_transports_config() == 0) {
      has_validated_pt = 1;
    }
  }

where has_validated_pt is a static variable. This means that after getting set to 1, validate_pluggable_transports_config() will never be called again (even after a SIGHUP).