The closure names used for builtin slots are mangled with their functype so
that overloaded C++ method names can be used for multiple slots.
For example:
%feature("python:slot", "mp_subscript", functype="binaryfunc") SimpleArray::__getitem__;
%feature("python:slot", "sq_item", functype="ssizeargfunc") SimpleArray::__getitem__(Py_ssize_t n);
will generate closures:
SWIGPY_SSIZEARGFUNC_CLOSURE(_wrap_SimpleArray___getitem__) /* defines _wrap_SimpleArray___getitem___ssizeargfunc_closure */
SWIGPY_BINARYFUNC_CLOSURE(_wrap_SimpleArray___getitem__) /* defines _wrap_SimpleArray___getitem___binaryfunc_closure */
Default hash is the underlying C/C++ pointer.
This matches up with testing for equivalence (Py_EQ in SwigPyObject_richcompare)
which compares the pointers.
If the wrong return type in the hash function was used, an error:
SystemError: error return without exception set
was raised
Add some tests for testing builtin slots
