Fix: wrong order of veget_max_cov variables from lcchange_main. Found by Chunjing
Fix: SnowDepth? must be defined to lower case
Change: make sure one of those methods from the subroutine thermosoil_getdiff are selected:
*use_toporganiclayer_tempdiff
*use_soilc_tempdiff -> default
Raise an exception if any of them is not selected