OGR VRT: *preliminary* work to be able to extend later the driver and format to support multiple geometry fields

git-svn-id: https://svn.osgeo.org/gdal/trunk@26981 f0d54148-0727-0410-94bb-9a71ac55c965
LIBKML: tries to identify a OFTDate field that matches the current OFTTime field

git-svn-id: https://svn.osgeo.org/gdal/trunk@26982 f0d54148-0727-0410-94bb-9a71ac55c965