Small improvements to argparse.

I've submitted these fixes upstream, let's hope they get included:

http://groups.google.com/group/argparse-devs/browse_thread/thread/2c03e4b3d28a3203

IPython/external/argparse.py

@@ -1169,8 +1169,7 b' class Namespace(_AttributeHolder):'
     """
 
     def __init__(self, **kwargs):
-        for name in kwargs:
-            setattr(self, name, kwargs[name])
+        self.__dict__.update(**kwargs)
 
     def __eq__(self, other):
         return vars(self) == vars(other)
@@ -1178,6 +1177,9 b' class Namespace(_AttributeHolder):'
     def __ne__(self, other):
         return not (self == other)
 
+    def __contains__(self, key):
+        return key in self.__dict__
+
 
 class _ActionsContainer(object):
 
@@ -2288,9 +2290,13 b' class ArgumentParser(_AttributeHolder, _ActionsContainer):'
     # Help-printing methods
     # =====================
     def print_usage(self, file=None):
+        if file is None:
+            file = _sys.stdout
         self._print_message(self.format_usage(), file)
 
     def print_help(self, file=None):
+        if file is None:
+            file = _sys.stdout
         self._print_message(self.format_help(), file)
 
     def print_version(self, file=None):