bpo-38392: PyObject_GC_Track() validates object in debug mode (GH-16615)

In debug mode, PyObject_GC_Track() now calls tp_traverse() of the
object type to ensure that the object is valid: test that objects
visited by tp_traverse() are valid.

Fix pyexpat.c: only track the parser in the GC once the parser is
fully initialized.
4 files changed