Allow spatial_file_get_wkt_features() to work during file validation

I need to parse some KML files during the file validation phase while uploading these files. I added some custom validation handler to a file_save_upload() call and want to parse the file for validation. The only trouble is that before the file is moved into it's final location it has no file extension. I need a way of forcing the spatial to know the file extension. Here is a patch!