Generating interpreter without dynsem.properties file leads to failure

[Eelco Visser]

Generating an interpreter without a dynsem.properties file in the project leads to failure instead of to a comprehensible error message.

[Vlad Vergu]

Thanks for opening. b8bfa1f introduces a warning in the editor if a dynsem.properties file is missing. The transformation (generate interpreter) now crashes with a comprehensible error message if the file is not present at generation time.