New XML schema for the GAW configuration

glite-api-wrapper (GAW) has just gotten a new XML Schema for the configuration file, starting from r1630. Documentation pages could be found here (a XML Schema documentation).

BTW, from now on we use a Xerces-C DOMBuilder interface to validate and parse GAW configurations.
DOMBuilder is an interface introduced by the W3C DOM Level 3.0 Abstract Schemas and Load and Save Specification. DOMBuilder provides the "Load" interface for parsing XML documents and building the corresponding DOM document tree from various input sources.