Fix for an obscure bug introduced by revs 46806 and 46808, with a test.

Fix for an obscure bug introduced by revs 46806 and 46808, with a test.
The problem of checking too eagerly for recursive calls is the
following: if a RuntimeError is caused by recursion, and if code needs
to normalize it immediately (as in the 2nd test), then
PyErr_NormalizeException() needs a call to the RuntimeError class to
instantiate it, and this hits the recursion limit again...  causing
PyErr_NormalizeException() to never finish.

Moved this particular recursion check to slot_tp_call(), which is not
involved in instantiating built-in exceptions.

Backport candidate.