Alternate viewpoints changes for RAWR tiles.

In tilezen/vector-datasource#1895, I added a little hack to work around the way we change the geometry type of `boundaries` layer features. They used to come entirely from the `planet_osm_polygon` table, but now we also include disputes and claims from `planet_osm_line`. However, we have to filter out a bunch of features from `planet_osm_line` that we don't want, but have the same tags as the polygons we do want.

Long story short: The query in `vector-datasource` sets this flag when transforming a polygon into a boundary line, so we have to do the same thing when reading from the RAWR tiles.

tilequeue/query/rawr.py

@@ -818,6 +818,10 @@ def _parse_row(self, zoom, unpadded_bounds, bbox, source, fid, shape,
                 # we don't want area on boundaries
                 read_row['__boundaries_properties__'].pop('area', None)
 
+                # set a flag to indicate that we transformed this from a
+                # polygon to a boundary.
+                read_row['mz_boundary_from_polygon'] = True
+
         if read_row:
             read_row['__id__'] = fid