Annotation processor should consider validators registered by XML constraint mapping

Background:
The Bean Validation API allows the set of validators for a given constraint to be specified/overridden using XML constraint mapping files (http://docs.jboss.org/hibernate/stable/validator/reference/en/html_single/#d0e1957).

Right now the annotation processor does not process any XML configuration files at all (neither validation.xml nor mapping files).

To do:
While it seems ok for now that the AP does not check constraint declarations given in XML (after all it's an annotation processor), I think it should evaluate the constraint definitions and the validators configured in XML. Otherwise the AP would raise false errors (as validators added in XML are ignored) or would give false positives (as validators given in @Constraint#validatedBy could be removed by "include-existing-validator='false'").