Revision 305

We want to keep the same variable names throughout procedures. In
pbl_surface, rain_fall and snow_fall were passed to clqh and became
precip_rain and precip_snow. Which name should we choose?
Precipitation normally refers to water in all phases. Rainfall and
snowfall seem to be more common names to distinguish liquid water and
snow. Cf. CF standard names. So change everywhere precip_rain to
rain_fall and precip_snow to snow_fall.