(PUP-2859) Specify call by position/name

We should reconsider this naming scheme. Call-by-name is already used in CS to refer to a lazy evaluation scheme (http://en.wikipedia.org/wiki/Evaluation_strategy#Call_by_name) and using that term here will cause confusion for anyone who knows this.  The proper terms for this are: positional arguments (or pass by position) and named arguments (or pass by name).