Revision 162

Variable pls of module pressure_var was only modified by calfis but I
could not move it to module calfis_m because it was used by a
procedure called by calfis (it would have been a cyclic
dependency). In the same way, variable p3d of module pressure_var was
only modified by leapfrog but I could not move it to module
leapfrog_m. So removed module pressure_var. p3d becomes a local
variable of leapfrog and an argument of calfis. Use paprs and play in
regr_pr_int and regr_pr_av (following LMDZ). The idea in regr_pr_int
and regr_pr_av is to spread and pack before the regridding instead of
packing afterward. The cost in memory should only be a two-dimensional
temporary array created by spread. The cost in clarity is only the
transiting of paprs and pplay through regr_pr_comb_coefoz, but this is
more than compensated by removing the side effect on module variables.