preprocessor: in stochastic mode, create auxiliary variables for exogenous with non-zero lead/lag
git-svn-id: https://www.dynare.org/svn/dynare/trunk@3026 ac1d8469-bf42-47a9-8791-bf33cf982152
git-svn-id: https://www.dynare.org/svn/dynare/trunk@3026 ac1d8469-bf42-47a9-8791-bf33cf982152