Parking should render over services area

[Grillmannen]

highway=services as an area denotes a rest area. In this rest area there is often parking for both cars and trucks. The parking nodes render over the services area, but not the parking area, which it in my opinion should.

Example: http://www.openstreetmap.org/#map=17/55.93934/12.81971

[matthijsmelissen]

In other words, amenity=parking areas should render on top of highway=services areas (if the amenity=parking area is smaller).

[matthijsmelissen]

Fixed by #743.