THe IncrementBy2 test type previously allowed any subtype including
floating point numbers. The meaning of this is actually a little unclear
and the feature was causing implicit type conversion warnings that were
hard to template out. The utility of of templating this class is dubious
in the first place, so class is now a fixed type.

I'm a little unsure whether we should keep this test class at all. It's
math operations are ad hoc and it could be difficult to determine if a
problem is caused by an actual problem or just bad math operators.