Revision 20

Deleted argument "presnivs" of "physiq", "ini_histhf", "ini_histhf3d",
"ini_histday", "ini_histins", "ini_histrac", "phytrac". Access it from
"comvert" instead.

Replaced calls to NetCDF Fortran 77 interface by calls to Fortran 90
interface or to NetCDF95.

Procedure "gr_phy_write_3d" now works with a variable of arbitrary
size in the second dimension.

Annotated use statements with "only" clause.

Replaced calls to NetCDF interface version 2 by calls to Fortran 90
interface in "guide.f90" and "read_reanalyse.f".

In "write_histrac", replaced calls to "gr_fi_ecrit" by calls to
"gr_phy_write_2d" and "gr_phy_write_3d".