This commit only introduce new elements in the Dynare language (adding the
possibility to decompose the target into stationary and non stationary
components) and insure that all the former codes (ie without decomposition of
the target) are still working as expected.
- Force long run levels of the exogenous variables to be zero or g (the BGP growth rate of the LHS endogenous variable).
- Fix the correction of the correction for the share λ (aak γ).
- Provisions for the case where the long run level of the exogenous variable is
different from 0 or g (see tmp1 and ll which should be added to the growth
neutrality correction as a constant).
(cherry picked from commit a4423d734e1df1d4ee09c7225d7fd610e0d94cd1)