Incoherent treatment of variables in method copy() of ProbNet

[Manuel Luque]

Method copy() in ProbNet was intelligently designed for keeping the original objects corresponding to variables when the new network is created. However, it makes an exception with decision criteria variable, because a new Variable object is created during the copy.

That incoherent behavior originates a mess, because the potentials in the new network reference to the original DecisionCriteria variable, but not to the new variable.

I suggest to be coherent in the copy method of ProbNet and leave as DecisionCriteria variable in the new network the object of the original network.