Product of the #pycon 2013 sprint with r.david.murray's assistance.  This implements the list of results as per tarek's suggested 1/ behavior in cases where ignore_errors=True.  Parameters accepted are not changed; return value is changed from None to an empty list in case of no errors or onerror defined by the user, and to a list of tuples exactly like onerror arguments in the case of ignore_errors=True.

As the ignore_errors=True closure-based implementation was adopted from test_shutil.py code, test_shutil.py is changed in one place to take advantage of the new return value in order to add coverage of the new functionality.