Improve display of decision rules with EXPECTATION operator
Currently, if the user inputs EXPECTATION(-1)(some_expr) in her model, then a new aux variable is created, and this var is a state var, which appears in the decision rules as EXPECTATION(-1)(...) (with the dots instead of the expression). This is not very informative. Displaying the full expression would require to add a new writeOutput method in the preprocessor.
And for something like EXPECTATION(-2)(some_expr), it is even worse, because there are 2 aux vars: one for the operator, and the second one which appears when removing lags of 2. It is the latter which appears in stoch_simul. Fixing this requires to fix the orig_endo field of M_.aux_vars in that case.