db.out.ogr Fails with bogus overwrite error

[micha]

The current script for db.out.ogr tests for existence of a file named as <input>.dbf. If the file exists and overwrite is not specified, the script exists. This test is performed even if the format is not dbf. So all of the other formats will fail if such a dbf file already exists, even though those formats do not touch the dbf file.

For the case of dbf output the script deletes all existing shapefile components (*.shp, *.shx) so the test is certainly necessary for dbf format. But I think it is unnecessary for the other formats.

Attached is a suggested diff.