Added returning of filled slice to FillATypes.
Added generated file as a test prerequisite in makefile.
Updated EqualATypes to handle comparisons to nil.

* Added check so that an empty slice does not equal nil.  Zero length
  does not differentiate these cases which may be important and are
  differentiated by the language (i.e. make([]Type, 0) != nil).
* Added special case for nil == nil.