An implementation of the SAX Locator interface that exposes the JDOM node being processed by SAXOutputter.

In JDOM2 this class is demoted to an interface. The information was never accurate anyway, and as an interface a specific Outputter instance can instead do 'the right thing' with the locator, if needed.

This change breaks a possible compatibility with anyone who happened to treat the JDOMLocator to be 'settable'. This used to extend LocatorImpl class which had setter methods for the ColumnNumber, Line, PublicID, SystemID