Problem with consecutive decisions in influence diagrams' inference

[Manuel Luque]

When executing inference with the attached network there is a Null pointer exception.

[Manuel Luque]

Miguel found the discrepancy between (1) the set of variables that VariableElimination wanted to eliminate a (2) the variables in the Markov network that stores the potentials. I decided to fix this problem from the VariableElimination class.