AFAICT, autoboxing/unboxing was added in Java 5 (September 30, 2004).
I think we can afford to use it. It should help us merge some Java
tests with the main ones.
However, beware that != does not unbox: it compares the object
addresses.
* examples/java/Calc.y, tests/java.at: Simplify.
* examples/java/Calc.test, tests/java.at: Improve tests.