WIP fix

Bug is fixed, but appears to have broken vision underwater. Notes:

+ basically fixed by darkening the colour of water such that it is
darker than refracted terrain
+ also disabled sunlight scattering at night. This may actually be
desirable, but given there is no visible moon it seems unlikely to make
much sense, and blends a lot of green into the water colour appearing
luminescent at night
Fixed underwater issue

I had accidentally deleted some interpolation parameters.
Merge remote-tracking branch 'filkry/bug640_luminescent_water'