homogeneize treatment of leads/lags on exogenous between deterministic and stochastic modes

Auxiliary variables are treated differently depending on the commands passed in the .mod file. As it stands now, if the following conditions hold

mod_file_struct.stoch_simul_present
mod_file_struct.estimation_present
mod_file_struct.osr_present
mod_file_struct.ramsey_policy_present
mod_file_struct.discretionary_policy_present
mod_file_struct.calib_smoother_present

we substitute endo and exo leads and lags. Otherwise, we only substitute endo leads and lags. This different treatment is undesirable for Julia output, where we will only use the preprocessor to process a model, without having the associated commands. In other words, we want the preprocessor model output to be same, regardless of the commands that are included outside of the model block.

As this change requires changes in the matlab code as well, the work will be done on the aux_func branch.