[Apply SF patch #504943]

This patch makes it possible to pass Warning instances as the first
argument to warnings.warn. In this case the category argument
will be ignored. The message text used will be str(warninginstance).
diff --git a/Misc/NEWS b/Misc/NEWS
index ada779e..4373f1a 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -70,6 +70,8 @@
 
 - distutils bdist commands now offer a --skip-build option.
 
+- warnings.warn now accepts a Warning instance as first argument.
+
 Tools/Demos
 
 Build