Fix reference leak in Py2 string comparison code when comparing str with unicode.

Cython/Utility/StringTools.c

@@ -235,6 +235,9 @@ static CYTHON_INLINE int __Pyx_PyUnicode_Equals(PyObject* s1, PyObject* s2, int
     } else {
         int result;
         PyObject* py_result = PyObject_RichCompare(s1, s2, equals);
+        #if PY_MAJOR_VERSION < 3
+        Py_XDECREF(owned_ref);
+        #endif
         if (!py_result)
             return -1;
         result = __Pyx_PyObject_IsTrue(py_result);