[BUG #6968] remove some unused code

- there is much more potential in lint.py to take advantage of the Hint()
  tree (e.g. see uses of 'get_at_hints').
- should make lint substantially faster
[BUG #6968] slight re-ordering of class methods
[BUG #6968] moved compile-time lint options to CodeMaintenance module
[BUG #6968] better debug logging for class cache
[BUG #6968] minor code clean-up
[BUG #6968] add Class.lint_check and use this in DependencyLoader

- Class.lint_check invokes lint and does caching via classCache
- DependencyLoader does the output of the lint warnings

- this still seems to be the best place to deliver these messgages, as the class
  list exploration is only done once
- at other places the warnings would be produced multiple times
[BUG #6968] bumped cache rev., as classCache has changed