don't allow a local class in a switch to capture a variable form the switch

javac fails the jacks test 16.2.3-switch-1. The offending code is something
like

        void f(int n) {
            switch (n) {
              case 12:
                final int x;
                x = 1;
                class Local {
                    int y = x;
                }
                break;
              case 13:
                int z = new Local().y; // verify error in generated code
            }
        }

The problem is that the JLS allows this code, but the variable x hasn't
been assigned at the point where it is captured.