Fixing of slicing errors ported to C++, parallelized.

xs/xsp/Print.xsp

@@ -112,6 +112,7 @@ _constant()
         %code%{ THIS->state.set_started(step); %};
 
     void _slice();
+    std::string _fix_slicing_errors();
     void detect_surfaces_type();
     void process_external_surfaces();
     void discover_vertical_shells();