tdf#50950 sort out Calc (ISO)WEEKNUM functions

[Winfried Donkers]

Hi Eike,

> The proper place to use that if the formula string is already compiled is
> in the RPN code generation formula/source/core/api/FormulaCompiler.cxx
> [...]
> All untried..

Thanks, I will try. 
You'll be informed of the results one way or the other ;)

Winfried