GenericHeaderAuthenticate.authenticate doesn't override superclass method

In JBossWeb 3, the types of the parameters of the Authenticator.authenticate method have changed. GenericHeaderAuthenticate overrides a superclass, and the change was made in the superclass but not in GenericHeaderAuthenticate. Effect is the method is no longer overridden, it's overloaded. Need to fix that.

This is the cause of the hudson failures in GenericHeaderAuthUnitTestCase (e.g. http://hudson.jboss.org/hudson/view/JBoss%20AS/job/JBoss-AS-6.0.x-testSuite-sun16/545/testReport/org.jboss.test.web.security/GenericHeaderAuthUnitTestCase/testGenericHeaderBaseAuth/)