Support PHPUnit 3.8+ compatibility

Summary:

PHPUnit 3.8+ adds a method to its PHPUnit_Framework_TestListener called addRiskyTest(). Need to stub it out to avoid "must implement this interface method" fatals when using 3.8+

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Blame Rev:
Merge pull request #2819 from JoelMarcey/3.1

Support PHPUnit 3.8+ compatibility