Oops. The value "0 or +1" for the category argument of PyErr_Warn()

doesn't work.  Make it 0.  (Although it really *should* be 0 or +1 --
the refcount is incremented when it is raised as an exception, but not
otherwise.)

Doc/api/refcounts.dat

@@ -207,7 +207,7 @@ PyErr_Format:char*:format::
 PyErr_Format::...::
 
 PyErr_Warn:int:::
-PyErr_Warn:PyObject*:category:0 or +1:
+PyErr_Warn:PyObject*:category:0:
 PyErr_Warn:char*:message::
 
 PyEval_AcquireLock:void:::