Fix #161: AbstractMiniboxedFunction serializable

abstract class AbstractMiniboxedFunction{0,1,2} extends Serializable

>>> Although this shouldn't be. But since they require arguments in the constructor,
the only solution is to make them serializable as well. Fortunately only anonymous
functions are rewired to `AbstractMiniboxedFunction`, so we're safe. Just for reference:

http://stackoverflow.com/questions/12125076/java-deserialization-invalidclassexception-no-valid-constructor