Quentin 01/03/2019: backup from commit 7d17f6da: the TINY function added on...

Quentin 01/03/2019: backup from commit 7d17f6da: the TINY function added on PURS lead to non-zero values to other variables such as convective precip. and snow variables such as T%TSNOW_ROOF%WSNOW in urban_snow_evol.F90 which lead to activate the snow cover 1layer model even if snow is not present