GML: upgrade driver to support Finnish NLS cadastral data and Inspire cadastral data. Add data/gml_registry.xml file to associate feature types with schemas. Extend .gfs syntax to be able to fetch OGR fields from XML attributes. Add support for multiple geometry columns (RFC 41)

git-svn-id: https://svn.osgeo.org/gdal/trunk@26591 f0d54148-0727-0410-94bb-9a71ac55c965