DOM4J implementation returns a null value in getParentAxis for document-level content

DOM4J Navigator returns inconsistent values for 'parent' type queries. Two types of issues exist:

1. Content at the document level (like COmments, PI's, etc.) have a null Navigator.getParentNode().
2. Content at the document level returns a null value in the getParentAxisIterator() which is illegal.

Attached is the XPathTestBase.java class which contains two new JUnit tests at the end... which test two concepts - Document content has Document parent, and that the content of getParentNode matches getParentAxisIterator.

These tests will fail until the DOM4J Navigator is fixed.... and, that looks a little complicated because, by my estimate, the DOM4J parsing process sets the Document-level content's parent to null... the Navigator will probably need a hack.