Fix false-positive for newer versions of Test::FailWarnings.

See:
 * http://www.cpantesters.org/cpan/report/2797d1f6-3900-11e3-bcab-a412b820295e
 * http://www.cpantesters.org/cpan/report/87c19344-6ec8-1014-8f73-5d205ce8bcae

These only occur with the more recent versions of Test::FailWarnings - 0.3
worked fine.