Issue #4910 (1st patch of a series): fix int() and the corresponding

PyNumber_Int/PyNumber_Long API function so that it no longer attempts
to call the __long__ method for conversion.  Only the __int__ and __trunc__
methods are used.  (This removes a major remaining use of the nb_long
slot from the Python 3.x core.)

Thanks Benjamin for review.

Lib/test/test_long.py

@@ -367,7 +367,7 @@ class LongTest(unittest.TestCase):
 
 
     def test_conversion(self):
-        # Test __long__()
+        # Test __int__()
         class ClassicMissingMethods:
             pass
         self.assertRaises(TypeError, int, ClassicMissingMethods())
@@ -410,18 +410,32 @@ class LongTest(unittest.TestCase):
         class Classic:
             pass
         for base in (object, Classic):
-            class LongOverridesTrunc(base):
-                def __long__(self):
+            class IntOverridesTrunc(base):
+                def __int__(self):
                     return 42
                 def __trunc__(self):
                     return -12
-            self.assertEqual(int(LongOverridesTrunc()), 42)
+            self.assertEqual(int(IntOverridesTrunc()), 42)
 
             class JustTrunc(base):
                 def __trunc__(self):
                     return 42
             self.assertEqual(int(JustTrunc()), 42)
 
+            class JustLong(base):
+                # test that __long__ no longer used in 3.x
+                def __long__(self):
+                    return 42
+            self.assertRaises(TypeError, int, JustLong())
+
+            class LongTrunc(base):
+                # __long__ should be ignored in 3.x
+                def __long__(self):
+                    return 42
+                def __trunc__(self):
+                    return 1729
+            self.assertEqual(int(LongTrunc()), 1729)
+
             for trunc_result_base in (object, Classic):
                 class Integral(trunc_result_base):
                     def __int__(self):