Preferential flow and sno file initialization
When initializing simulations with preferential flow, the sno file should contain a column with the volumetric contents in preferential flow (Vol_Frac_WP), directly following Vol_Frac_W. If this is not done, initialization behaviour is unexpected (snow layers are ignored, soil layers are not being recognized as such) and inconsistent error messages are given. A proper check needs to be implemented.