FWIW, I just got this to work with hibernate-validator-4.0.0.Beta1. I had to add the following files to the WEB-INF/lib directory:
hibernate-validator-4.0.0.Beta1.jar, lib/slf4j-log4j12-1.5.6.jar, lib/log4j-1.2.14.jar, lib/slf4j-api-1.5.6.jar, lib/validation-api-1.0.CR2.jar
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