Construct ErrorHandler with kwargs instead of positional arguments

for consistency with normal handler construction (and compatibility with
the initialize() changes from a couple of commits ago).

Closes #194.

tornado/web.py

@@ -1160,7 +1160,7 @@ class Application(object):
                         args = [unquote(s) for s in match.groups()]
                     break
             if not handler:
-                handler = ErrorHandler(self, request, 404)
+                handler = ErrorHandler(self, request, status_code=404)
 
         # In debug mode, re-compile templates and reload static files on every
         # request so you don't need to restart to see changes