avoid error because of missing timezone info in pure date objects

git-svn-id: svn://svn.cy55.de/Zope3/src/loops/trunk@4187 fd906abe-77d9-0310-91a1-e0d9ade77398

browser/resource.py

@@ -200,7 +200,7 @@ class ResourceView(BaseView):
         modified = self.modifiedRaw
         if modified:
             format = '%a, %d %b %Y %H:%M:%S %Z'
-            if modified.tzinfo is None:
+            if getattr(modified.tzinfo, None) is None:
                 format = format[:-3] + ' GMT'
             response.setHeader('Last-Modified', modified.strftime(format))
         return data