Warn people away from PyModule_GetDict(), but not too strongly.

(The real issue is whether modules can benefit from an alternate
implementation strategy rather than using a dictionary.  We should migrate
away from direct dictionary manipulation to allow more room for Jeremy to
flex the implementation with changes in globals lookup.)

Doc/api/concrete.tex

@@ -2111,6 +2111,9 @@ There are only a few functions special to module objects.
   namespace; this object is the same as the \member{__dict__}
   attribute of the module object.  This function never fails.
   \withsubitem{(module attribute)}{\ttindex{__dict__}}
+  It is recommended extensions use other \cfunction{PyModule_*()}
+  and \cfunction{PyObject_*()} functions rather than directly
+  manipulate a module's \member{__dict__}.
 \end{cfuncdesc}
 
 \begin{cfuncdesc}{char*}{PyModule_GetName}{PyObject *module}