The latest boxing spec filed under CCC 4989021 requires an implementation
to cache boxed values in the range -128 to 127.  The following test case
for this property fails, showing that we don't cache.

class CacheBox {
    public static void main(String[] args) {
        Integer i1 = 12;
        Integer i2 = 12;
        if (i1 != i2) throw new Error();
    }
}