Fix unintentional skipping of module level doctests Importing `skip_doctest` decorator unintentionally marks for skipping a module level doctest. It happens because doctests discovery only checks whether a variable with name `skip_doctest` is presented without checking the type. I have renamed the 'magic' variable name to `__skip_doctest__` to resolve the name clash, and also made the check actually depend on the variable content. The module level doctest in `core/debugger.py` was previously unintentionally skipped and now is disabled because it contains syntax/name errors.