array(int, null) returns null. Purpose: Builtin can be better used for
casts. Developer does not have to test for null value.

Changed builtin repr() for types:
typeof((int)) => typeof((System.Int32))
typeof((int,3)) => typeof((System.Int32, 3))
List[of int] => System.Collections.Generic.List[of System.Int32]

This will make it easier for newbies to learn how to deal with types in BOO (I know this from experience)