Incorrect error message

[SiggyF]

This function suggests that a recursion errorr is present. But that's not always the case. If you add invalid activities you also end up here. Make the error more clear and provide the list of unregistred items to the user so they can solve their problem more quickly.

OpenCLSim/src/openclsim/model/helpers.py

Line 47 in 92411c2

raise ValueError(

[SiggyF]

Also raise the logging level to warn so that the errors show up by default.