Review of trunk r4525 (TypeNode::getBaseType()):

Review of trunk r4525 (TypeNode::getBaseType()):

* fixed TypeNode::getBaseType() for predicate subtypes
* added Type::getBaseType() for public interface
* added unit testing

To avoid confusion, also:

* renamed PredicateType::getBaseType() to "getParentType()"
* renamed TypeNode::getSubtypeBaseType() to "getSubtypeParentType()"

(this commit was certified error- and warning-free by the test-and-commit script.)