postgis geometry type detection - fall through to detecting type on individual geometries if the geometry_columns only reports 'geometry' - refs mapbox/tilemill/#2099

plugins/input/postgis/postgis_datasource.cpp

@@ -1026,8 +1026,7 @@ boost::optional<mapnik::datasource::geometry_t> postgis_datasource::get_geometry
                     }
                     else // geometry
                     {
-                        result.reset(mapnik::datasource::Collection);
-                        return result;
+                        g_type = "";
                     }
                 }
             }