ipdb: rename the method to `shadow()`
ipdb: chaining of transactional object operations

So the operations changing state of an object will return the object itself also,
allowing operation chains, like that::
	ip.create(ifname='bo0', kind='bond').\
		add_port(port1).\
		add_port(port2).\
		ip_add('172.16.0.1/24').\
		ip_add('172.16.0.2/24').\
		commit()

Just a syntactical sugar in the functional-like manner.