Rework the #dnu benchmarks to do consistently the same thing

- we do pass a parameter and do an if test on it in order to see the parameter passing overhead consistently
- we check the result to make sure that we get the expected behavior
- we have now the following five benchmarks:
   1. DirectAdd: baseline performance, no reflective operations involved
   2. DnuAdd:    using the indirection via the #dnu handler to perform the #inc: operation directly, only #dnu overhead, otherwise no reflective operations
   3. PerformAdd: using #perform: to invoke #inc:, no other reflective operations
   4. DnuPerfomAdd: using the #dnu handler and #perform: but having a literal #inc: in the #dnu
   5. ProxyAdd: fully reflective proxy implementation via #dnu: but requires additional proxy object

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Added IndirectAdd to compare directly with ProxyAdd

IndirectAdd does use also a second object, but no reflection.

Signed-off-by: Stefan Marr <git@stefan-marr.de>