tp_new must always be generated to set the vtab

but we can get away with skipping intermediate classes if nothing new happens

Cython/Compiler/ModuleNode.py

@@ -610,8 +610,6 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
     def generate_new_function(self, scope, code):
         tp_slot = TypeSlots.ConstructorSlot("tp_new", '__new__')
         slot_func = scope.mangle_internal("tp_new")
-        if tp_slot.slot_code(scope) != slot_func:
-            return # never used
         type = scope.parent_type
         base_type = type.base_type
         py_attrs = []

Cython/Compiler/TypeSlots.py

@@ -643,7 +643,7 @@ slot_table = (
     
     MethodSlot(initproc, "tp_init", "__init__"),
     EmptySlot("tp_alloc"), #FixedSlot("tp_alloc", "PyType_GenericAlloc"),
-    ConstructorSlot("tp_new", '__new__'),
+    InternalMethodSlot("tp_new"),
     EmptySlot("tp_free"),
     
     EmptySlot("tp_is_gc"),