Fix tabs and utf-8 quotes in source code
Some VTK source code still had tabs (even some of the .py files!). Also, several comments used utf-8 quotes, which are hard to tell from regular quotes by eye and can lead to confusing mistakes.
Some VTK source code still had tabs (even some of the .py files!). Also, several comments used utf-8 quotes, which are hard to tell from regular quotes by eye and can lead to confusing mistakes.