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.