[Ili] Consistent modelFilename const type

git-svn-id: https://svn.osgeo.org/gdal/trunk/gdal@27184 f0d54148-0727-0410-94bb-9a71ac55c965
[Ili] Use tr_strdup from gml driver instead of XMLString::transcode

git-svn-id: https://svn.osgeo.org/gdal/trunk/gdal@27185 f0d54148-0727-0410-94bb-9a71ac55c965