Fix accidental usage of PyFrozenSet_New() in PyPy.

CHANGES.rst

@@ -2,6 +2,19 @@
 Cython Changelog
 ================
 
+0.28.1 (2018-0?-??)
+===================
+
+Features added
+--------------
+
+Bugs fixed
+----------
+
+* ``PyFrozenSet_New()`` was accidentally used in PyPy where it is lacking
+  from the C-API.
+
+
 0.28 (2018-03-13)
 =================
 

Cython/Utility/ObjectHandling.c

@@ -1049,6 +1049,7 @@ static CYTHON_INLINE int __Pyx_PyDict_ContainsTF(PyObject* item, PyObject* dict,
 static CYTHON_INLINE int __Pyx_PySet_ContainsTF(PyObject* key, PyObject* set, int eq); /* proto */
 
 /////////////// PySetContains ///////////////
+//@requires: Builtins.c::pyfrozenset_new
 
 static int __Pyx_PySet_ContainsUnhashable(PyObject *set, PyObject *key) {
     int result = -1;
@@ -1056,7 +1057,7 @@ static int __Pyx_PySet_ContainsUnhashable(PyObject *set, PyObject *key) {
         /* Convert key to frozenset */
         PyObject *tmpkey;
         PyErr_Clear();
-        tmpkey = PyFrozenSet_New(key);
+        tmpkey = __Pyx_PyFrozenSet_New(key);
         if (tmpkey != NULL) {
             result = PySet_Contains(set, tmpkey);
             Py_DECREF(tmpkey);

Cython/Utility/Optimize.c

@@ -486,6 +486,7 @@ static CYTHON_INLINE int __Pyx_set_iter_next(
 }
 
 /////////////// py_set_discard_unhashable ///////////////
+//@requires: Builtins.c::pyfrozenset_new
 
 static int __Pyx_PySet_DiscardUnhashable(PyObject *set, PyObject *key) {
     PyObject *tmpkey;
@@ -494,7 +495,7 @@ static int __Pyx_PySet_DiscardUnhashable(PyObject *set, PyObject *key) {
     if (likely(!PySet_Check(key) || !PyErr_ExceptionMatches(PyExc_TypeError)))
         return -1;
     PyErr_Clear();
-    tmpkey = PyFrozenSet_New(key);
+    tmpkey = __Pyx_PyFrozenSet_New(key);
     if (tmpkey == NULL)
         return -1;
     rv = PySet_Discard(set, tmpkey);