Get rid of globals in make_ex_
Their presence creates a bunch of issues. In dfc89df6 we added a call to
make_ex_ to make the
tests/forecast/Hansen_exo_det_forecast.mod run. But then 105100c7 eliminated the globals from
dyn_forecast, splitting the workspace of globals used within
dyn_forecast from the one set by
make_ex_, thereby breaking the unit test.