SFCWater Changes

canopy_struct_dynamics:
- Reverted the use of snowfall back to a previous definition based on
canopy height. Current implementation of snowfall (% ground covered in
snow) lead to occasional canopy CO2 problems in young patches.  This
needs to be looked at in greater depth.

rk4_derivs:
- h_flux between snow & ground shouldn’t be scaled by %snow cover since
it’s all on a per m2 basis
- we need the h_flux for a layer above the snow (mirrors the ground &
an older version of ED) otherwise we end up with weird things happening
to the between-layer heat transfers

rk4_misc
- I changed the rules for creating additional layers.  New version
requires snow layers to meet stability requirements for mass, energy, &
depth.  (Previous version ignored depth explicitly which lead to some
strange layer energetics.)
Commented out mean_diel -- Don't pull!

This one shouldn’t be merged with the master branch!
I haven’t dug into this, but it was trying to evaluate qmean_can_prss
which didn’t exist and would cause a segfault crash even though I don’t
think I was writing the diurnal cycle, so I just commented this out.