[Flow] XForm.finish unnecessarily removes session

[Ugo Cei]

In the Flow's system.js script, the function XForm.finish calls 
cocoon.removeSession(). This is a problem when you're using a session 
for other purposes, like for holding a user's profile after 
authentication. In this case, calling XForm.finish has the effect of 
logging out the user.

Is removing the session really necessary?

	Ugo