write warning into generated header file for now to explain that calling the...

write warning into generated header file for now to explain that calling the module init function is not enough to initialise the module anymore

Cython/Compiler/ModuleNode.py

@@ -201,6 +201,9 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
             h_code.putln("")
             h_code.putln("#endif /* !%s */" % api_guard)
             h_code.putln("")
+            h_code.putln("/* WARNING: the interface of the module init function changed in CPython 3.5. */")
+            h_code.putln("/* It now returns a PyModuleDef instance instead of a PyModule instance. */")
+            h_code.putln("")
             h_code.putln("#if PY_MAJOR_VERSION < 3")
             h_code.putln("PyMODINIT_FUNC init%s(void);" % env.module_name)
             h_code.putln("#else")