[Dart-users] minor update to wrf model_mod.f90

[Nancy Collins]

dart/wrf users:

i've just committed a minor update to the wrf model_mod.f90.
if you add soil variables to your state vector, it was not computing
the right vertical stagger size, which would be used when writing
out the arrays in the diagnostic files.   (the assimilation itself would
not be affected).

we also removed the soil_data logical from the domain derived type,
because it has no affect on the code anymore.  both it and h_diab
should be removed from the namelist at some point, but since it is
a backwards-incompatible change we haven't done it yet.

thanks to greg for finding the stagger inconsistency, and thanks to
josh for fixing it.

nancy