[CONFIGURATION-573] ConfigurationNodeIteratorAttribute now supports namespaces.

Namespace prefixes are now handled when iterating over the attributes of a
node. Some common functionality was refactored into the base class.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1591091 13f79535-47bb-0310-9956-ffa450edef68
[CONFIGURATION-573] Added a test for namespaces.

The test checks whether XPathExpressionEngine now handles expressions
referencing nodes and attributes with namespaces correctly.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1591092 13f79535-47bb-0310-9956-ffa450edef68