SF bug 994255: Py_RETURN_NONE causes too much warnings

Rewrote Py_RETURN_{NONE, TRUE, FALSE} to expand to comma expressions
rather than "do {} while(0)" thingies.  The OP complained because he
likes using MS /W4 sometimes, and then all his uses of these things
generate nuisance warnings about testing a constant expression (in
the "while(0)" part).  Comma expressions don't have this problem
(although it's a lucky accident that comma expressions suffice for these
macros!).

Include/boolobject.h

@@ -24,8 +24,8 @@ PyAPI_DATA(PyIntObject) _Py_ZeroStruct, _Py_TrueStruct;
 #define Py_True ((PyObject *) &_Py_TrueStruct)
 
 /* Macros for returning Py_True or Py_False, respectively */
-#define Py_RETURN_TRUE do {Py_INCREF(Py_True); return Py_True;} while (0)
-#define Py_RETURN_FALSE do {Py_INCREF(Py_False); return Py_False;} while (0)
+#define Py_RETURN_TRUE return Py_INCREF(Py_True), Py_True
+#define Py_RETURN_FALSE return Py_INCREF(Py_False), Py_False
 
 /* Function to return a bool from a C long */
 PyAPI_FUNC(PyObject *) PyBool_FromLong(long);

Include/object.h

@@ -650,7 +650,7 @@ PyAPI_DATA(PyObject) _Py_NoneStruct; /* Don't use this directly */
 #define Py_None (&_Py_NoneStruct)
 
 /* Macro for returning Py_None from a function */
-#define Py_RETURN_NONE do {Py_INCREF(Py_None); return Py_None;} while (0)
+#define Py_RETURN_NONE return Py_INCREF(Py_None), Py_None
 
 /*
 Py_NotImplemented is a singleton used to signal that an operation is