Handle large bounding box changesets better

If the bounding box of a changeset is much larger than the map then
there seem to be problems with OL not rendering the feature correctly
so reduce the highlight to just be the extent of the map plus a small
margin in that case.

app/views/changeset/_map.html.erb

@@ -14,6 +14,10 @@
     var feature = vectors.getFeatureByFid(id);
     var bounds = feature.geometry.getBounds();
 
+    if (bounds.containsBounds(map.getExtent())) {
+      bounds = map.getExtent().scale(1.1);
+    }
+
     if (highlight) vectors.removeFeatures(highlight);
 
     highlight = new OpenLayers.Feature.Vector(bounds.toGeometry(), {}, {