Adding support to default integer return values

Implementing issue #95, for now adding support only for integers. If i is ok we can move on to other data types.
I find this to be subjective, but i really find odd that the name of the value is related to the fact that it has no value defined on it. To cause some bizarre problem all i have to do it create a MockNamedValue with the name "" and a value inside it. To reproduce the problem try to test a nameless function :-). Since the case does not seems to be something that will happen on real life it is not that big deal...but i still find it odd.