filelisterrordialog: Make _addFileExpander a private static method.
filelisterrordialog: break comment too long.
filelisterrordialog: add docstrings.
prefs: Switch to new style class
prefs.py: Docstring fixes.
prefs: Split line too long.
prefs: Run tests if run standalone.

Instead of having to manually set False to True.
prefs: prefix regex string with 'r'