(cherry picked from commit 3580a7c0)

* R4 are now written in netCDF files as simple precision
* files can be read even if written with different integer or real precisions
* new attributes for netCDF files: MNH_REAL and MNH_INT
* several small bug corrected

Philippe 06/06/2018: IO: renamed CLTOPCONV and CLBASCONV to CLTOPCONV_LVL and CLBASCONV_LVL (fields with same names but different metadata are written by DIAG)

Juan 24/05/2018: COUPLING , in oasis3-mct_v3.tar.gz/make.gfortran_mesonh add ?= to managed correctly NETCDF_INCLUDE/NETCDF_LIBRARY from Makefile.MESONH.mk

Juan 24/05/2018: COUPLING , minor correction for 013_Iroise_ideal_case_coupling , +1 dim in variables & rm old files

Juan 24/05/2018: COUPLING , introduce new LMNH_ISINIT variable to initialise correctly MNH with INIT_NMNH_COMM_WORLD in coupled run

Philippe 31/05/2018: IO: added TNCOORDS field to TFILEDATA to point correctly to coordinates variables