- in additon allow Py_TPFLAGS_HAVE_VERSION_TAG because even though we don't use it this flag shouldn't cause problems
- allow tp_del because AFAIK it's implemented.
- allow calling methods which specify METH_COEXIST because it doen't make a difference for the call
- disable PyCode_New call inside cython because we don't support it yet and it's unused.
- change cython to use PyCFunction_Call instead of the custom version it has for pypy