[fpc-pascal] Adding method dynamically to a class

[Marco van de Voort]

In our previous episode, kyan said:
> I suggest that you implement this using interfaces. You place the
> interface declaration in a common file, use the interfaces from the
> main exe but implement them in separate dlls.

Or maybe go a step further, and use IDispatch that passes through unknown
methods to handler functions in the loaded dynamic libraries.

This will also allow some freedom in the parameter lists of added functions.