Revision 279

fqcalving was saved in physiq and had intent inout in pbl_surface. So
we could set fqcalving to 0 only once per run. The point is fqcalving
must be defined everywhere for the computation of the average over all
surfaces, even values that get multiplied by pctsrf = 0. I find it
clearer to set fqcalving to 0 at every call of pbl_surface. This is
more expensive but allows to give intent out to fqcalving in
pbl_surface and remove the save attribute in physiq.

Add zxfqcalving output netCDF variable (following LMDZ).