POLYLINE: changed the return type for dxf_polyline_read().

Signed-off-by: bert <bert.timmerman@xs4all.nl>
POLYLINE: use DxfFile struct.

Signed-off-by: bert <bert.timmerman@xs4all.nl>
POLYLINE: make strings translatable.

Signed-off-by: bert <bert.timmerman@xs4all.nl>
POLYLINE: added dxf_polyline_free().

Signed-off-by: bert <bert.timmerman@xs4all.nl>