XACML schema validation, as some of them were not XACML 3.0 compliant.
* New class DatatypeConstants to centralized all standard datatype
constants
* Generalized the notion of Expression value and datatype to bags
(formerly restricted to primitive datatypes) - new class BagDatatype
* Addded Bags utils class equivalent to Collections class to create
empty bag, singleton bag, etc.
* Removed xmlbeans dependency (replaced by use of Saxon for same
features)
* Improved logs in Rule evaluation
* Improved hashCode/equals/toString methods in most classes
* Fixed variable management: remove Policy-locally-defined variables
from context when done evaluating the policy
* Better management of Policy versions, in particular for
PolicyIdReference resolution
* Modified BooleanAttributeValue to avoid creating new instances of it
during evaluation