In working on issue 11250, I noticed that lib2to3's test_parser.py tests were not enabled.  Fixing that was easy enough, but then test_all_project_files() in TestParserIdempotency began failing.  I've shaved enough yaks for the day so I am going to leave test_parser enabled but mark test_all_project_files() with @expectedFailure.

Note that there are a number of failures here. There are two ParseErrors, one in main.py and one in pytree_idempotency.py.  These both seem to fail on print(..., file=foo).  After that, bom.py fails idempotency because the BOM does not show up in the converted file.