Check if Fortran interface is complete

Check whether the Fortran interface covers the C++ interface.

setAdditionalData is one particular missing function, whose interface can be somewhat tricky, due to its polymorphic nature.

One way is to write an interface for each possible usage variant that all translate to the same void* C function. The problem here is the object functions, which cannot access an interface written in the same module.

The other way is to simply have separate functions for the separate load balancer methods.

The third way to investigate is a type(*) dummy argrument, which may or may not be Fortran 2003 compatible.