Introduced a Py_IS_NAN macro, which probably works on the major platforms
today.  pyconfig.h can override it if not, and can also override
Py_IS_INFINITY now.  Py_IS_NAN and Py_IS_INFINITY are overridden now
for Microsoft compilers, using efficient MS-specific spellings.
diff --git a/Misc/NEWS b/Misc/NEWS
index 89a6c57..d3f4fe4 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -74,7 +74,11 @@
 Build
 -----
 
-...
+- pyport.h now defines a Py_IS_NAN macro.  It works as-is when the
+  platform C computes true for ``x != x`` if and only if X is a NaN.
+  Other platforms can override the default definition with a platform-
+  specific spelling in that platform's pyconfig.h.  You can also override
+  pyport.h's default Py_IS_INFINITY definition now.
 
 C API
 -----