Based on the experience from bug #611176, we should: 1. make the eclasses re-export generated vars on each inherit of eclass (i.e. move them outta guards), 2. optionally check for changing control variables and bail out whenever that happens (to avoid surprise when eclass silently overrides ebuild), 3. optionally improve error messages from python_setup&co. to more clearly indicate what failed.
Ok, 1. is a kinda no-go since we are making the variables readonly, and therefore no further inherit can modify them.
I think this was already solved. After all, we do have integrity checks in place.
