Added some explanatory comments.
Reverted to default errors array if no errors are defined.

This way _list/bbox-filter/geojson could also be queried I hope.
Adding spatial relations to _list/bbox-filter.
Added "contains" to options.relation.

This requires a GeoJSON object of type Polygon or MultiPolygon or
GeometryCollection in req.body. A GeometryCollection should of course have
polys in it because anything else will be ignored.
Provided for options.relation and undefined req.body.GeoJSON.

This makes sense because the list function always checks for intersecting
bboxes where I might also need 'contains' and 'within'.
Changed _list/bbox-filter to load lib/utils only if needed.
Changed point-in-polygon checks to restart from center.

My point-in-polygon test is not written in a very secure way: If a point falls
right on a line segment, it may return an inverted value. This avoids that one
screwed up test translates through all the rows following it.
Un-stripped last coord from req.body.GeoJSON.

Because view/geojson always provides stripped polys.