Preprocessor update

–  ramsey_policy: lift restriction that order must be ⩽ 2
–  Extend incompatibility with deterministic exogenous to ramsey_model command
–  Incorrect stochastic transformation with endo lead ⩾ 2 or exo lead ⩾ 1 in external functions
–  Crash when writing the (static) set_auxiliary_variables file in the presence of external functions

preprocessor @ d1e9f253

-Subproject commit e4c8b2d6422e8617d707d3d31a76a53e3a1b283d
+Subproject commit d1e9f253940b9925a0c9dd8eb53345555b6d6e54