IBM-DM-019: No need for orphan namespace nodes

Data Model Section 6.4.1 (Namespace Nodes--Overview): This section states 
that the data model permits namespace nodes without parents (parent 
property may be empty). This should be changed. There is no longer a 
namespace node constructor in XQuery. There is no way to create a 
namespace node independently of an element node, and no reason why the 
data model should permit this.