Changeset 3451

bugfix to prevent TeDBF from getting extinct when impose_CN=false using a restart from impose_cn=true:
we need to fill the reserve nitrogen stocks up to allow them to built leaves and roots in the first year.

conceptual modification:
Following Zaehle & Friend (2010) I make trees to store C,N,P for all of their next years roots.
The 30% coverage is too risky imo and defoliation experiments show that leaf store enough resources to built more than one set of leaves.

DSG