Analysis: the primary recursion error is correctly raised, but then
there is a call to PyErr_NormalizeException, which calls
PyEval_CallObject, which increases the stack depth and hit the recursion
limit again...
python2.5 don't have the problem because PyEval_CallObject did not check
the recursion limit.

Different solutions I can think of:
- use a prebuilt exception: not possible if we still want an error
message containing the context.
- in PyErr_NormalizeException, "PyEval_CallObject" is too generic. We
could have a special path for exception types deriving from
BaseException: directly call the constructor.