Add ogr2ogr option to avoid automatic fid detection to example config

Loader currently exposes the fid as an element, GDAL/OGR 1.10 now
correctly auto detects a fid attribute and exposes it. When using
GDAL/OGR 1.10 an additional fid2 column is created by OGR. In future
once support for GDAL/OGR 1.10 is widespread we can probably avoid
having Loader expose the fid and let OGR handle it but for now allow
Loader to handle it to avoid having a dependency on a fairly recent
version of GDAL/OGR.

python/loader.config

@@ -25,7 +25,7 @@ tmp_dir=/path/to/temp/folder
 #   $output_dir - the directory specified by the out_dir setting
 #   $base_file_name - the file name of the file to be loaded
 #   $file_path - the full path of the file to be loaded
-ogr_cmd=ogr2ogr -append -skipfailures -f PostgreSQL PG:'dbname=postgis active_schema=public host=localhost user=postgres password=postgres' $file_path
+ogr_cmd=ogr2ogr --config GML_EXPOSE_FID NO -append -skipfailures -f PostgreSQL PG:'dbname=postgis active_schema=public host=localhost user=postgres password=postgres' $file_path
 
 # The command used to prepare the source
 # data so it is suitable for loading with OGR. Choose a prep