Pierre-Yves David <pierre-yves.david@logilab.fr> [Thu, 27 Jun 2013 12:02:38 +0200] rev 9112
[connection] enforce that a connection must be open to be used
The same than for ClientConnection, we ensure the connection is used inside a
its context.
.. note:: We may rely on that for ClientConnection and remove de dedicated code
in Client Connection but I prefer the current explicite and duplicated
version for now.