Cherry-pick "Merge branch 'PythonCompilation-master-20170815' into 'master'" into 1.0

Python Byte-compilation During Build, master branch (2017.11.03.)

See merge request !164 (merged)

I've pondered about this quite a bit. But by now I decided that the 21.X branches should be kept clean of Python syntax errors as well. And since for instance for AnalysisBase-21.2 I only had to fix 1 error, I think it should be manageable to clean up all of the 21.X branches.