Fix rollercoasters

While diving into #1951 I noticed that the roller coaster exception in ImportDatabase_Prepare is wrong. 

attraction=roller_coaster does refer to the area where the entire roller coaster is located (see wiki: https://wiki.openstreetmap.org/wiki/Tag:attraction%3Droller_coaster ). Consequently, it must be a polygon (or a node).

For the track, the tag roller_coaster=track (https://wiki.openstreetmap.org/wiki/Tag:roller_coaster%3Dtrack) has to be used. The wiki's both explicitly state that this tag should not be combined with attraction=roller_coaster. The track is of course not a polygon, even if it's a closed loop.

note that this exception was added almost 12 years ago, when roller_coaster=track didn't exist yet.

osmosis/ImportDatabase_Prepare.sql

@@ -15,7 +15,7 @@ BEGIN
       ST_IsValid(NEW.linestring) AND
       ST_IsSimple(NEW.linestring) AND
       ST_IsValid(ST_MakePolygon(NEW.linestring)) AND
-      NOT (NEW.tags?'attraction' AND NEW.tags->'attraction' = 'roller_coaster');
+      NOT (NEW.tags?'roller_coaster' AND NEW.tags->'attraction' = 'track');
   END IF;
   RETURN NEW;
 END;