Variable elimination algorithm doesn't return the appropriate message when there are numerical variables

[Manuel Luque]

Variable elimination algorithm doesn't return the appropriate message when there are numerical variables in the network. The message should be something like "The network is not evaluable...", and not write anything in the console.

[Manuel Luque]

Variable elimination algorithm returns now the exception message and this is presented in the GUI. The behaviour of the GUI has not been modified and then, after showing the message, the inference panel is presented to the user.