Add ipython shell command

This command allows you to start an IPython shell running directly in circusd. It exposes ``arbiter`` as a local variable, so you can do this, for instance:

	> circusctl ipython
	Python 3.3.3 (default, Nov 19 2013, 18:24:35)
	Type "copyright", "credits" or "license" for more information.
	
	IPython 1.2.0 -- An enhanced Interactive Python.
	?         -> Introduction and overview of IPython's features.
	%quickref -> Quick reference.
	help      -> Python's own help system.
	object?   -> Details about 'object', use 'object??' for extra details.
	
	In [1]: arbiter.statuses()
	Out[1]:
	{'logger': 'active',
	 'plugin:flapping': 'active',
	 'plugin:monitor': 'active',
	 'sf': 'active',
	 'web-server': 'active'}
	
	In [2]:

We are running into a memory leak at the moment in our circusd instances. We'll use this to connect to a greedy instance and inspect the ``gc``.