add warning for mro inhereitance class issues

Author: Eddy Xu

Lib/test/test_py3kwarn.py

@@ -474,7 +474,7 @@ class D(B, C):
             self.assertEqual(D().do_this(), "A")
             self.assertMROWarning(
                 w,
-                "classic multiple inheritance for class 'D' may resolve "
+                "classic multiple inheritance for class 'D' will resolve "
                 "attribute 'do_this' from 'A' in 2.x but from 'C' in 3.x "
                 "due to C3 MRO")
 
@@ -571,7 +571,7 @@ class D(B):
             self.assertEqual(D().do_this(), "A")
             self.assertMROWarning(
                 w,
-                "classic multiple inheritance for class 'D' may resolve "
+                "classic multiple inheritance for class 'D' will resolve "
                 "attribute 'do_this' from 'A' in 2.x but from 'C' in 3.x "
                 "due to C3 MRO")
 

Objects/classobject.c

@@ -353,7 +353,7 @@ warn_mro_resolution_change(PyClassObject *klass,
     }
 
     msg = PyString_FromFormat(
-        "classic multiple inheritance for class '%s' may resolve attribute '%s' "
+        "classic multiple inheritance for class '%s' will resolve attribute '%s' "
         "from '%s' in 2.x but from '%s' in 3.x due to C3 MRO",
         class_name_cstr(klass),
         PyString_AsString(name),