Warning: not fully tested

+ removed some LEN=LEN_HREC for unrelated variables

+ removed unused variables

It was already possible but LEN_HREC was missing in some places.

Done to prevent problems later

* added IO_READ_FIELD_BYNAME_N1 and IO_READ_FIELD_BYFIELD_N1 subroutines
  to IO_READ_FIELD procedure
* added IO_READ_FIELD_LFI_N1 subroutine to IO_READ_FIELD_LFI procedure
* added IO_READ_FIELD_NC4_N1 subroutine to IO_READ_FIELD_NC4 procedure

Philippe 18/08/2017: IO: use IO_READ_FIELD for several fields, IO_FILE_OPEN and IO_FILE_CLOSE for several files

Philippe 18/08/2017: IO: IO_FILE_ADD2LIST manage the case in which a file is already in the filelist (with an optional argument)

Philippe 18/08/2017: IO: added NOPEN_CURRENT to TFILEDATA type to allow multiple concurrent openings of a given file

Philippe 18/08/2017: IO: IO_READ_FIELD read fields even if CFORMAT=LFICDF4 (and therefore file opened in WRITE mode)

* added IO_READ_FIELD_BYNAME_N2/L1 and IO_READ_FIELD_BYFIELD_N2/L1 subroutines
  to IO_READ_FIELD procedure
* added IO_READ_FIELD_LFI_N2/L1 subroutines to IO_READ_FIELD_LFI procedure
* added IO_READ_FIELD_NC4_N2/L1 subroutines to IO_READ_FIELD_NC4 procedure

Warning: there is a netCDF/HDF5 bug (HDF5/1.8.9 and netCDF/4.1.3)
Works with HDF5/1.8.19, netCDF-C/4.4.1.1 and netCDF-fortran/4.4.4

* added IO_READ_FIELD_BYNAME_X3 and IO_READ_FIELD_BYFIELD_X3 subroutines
  to IO_READ_FIELD procedure
* added IO_READ_FIELD_LFI_X3 subroutine to IO_READ_FIELD_LFI procedure
* added IO_READ_FIELD_NC4_X3 subroutine to IO_READ_FIELD_NC4 procedure
* check all dimensions instead of total size when reading a field
  in netCDF files

* added IO_FILE_ADD2LIST subroutine and use it
* IO_FILE_OPEN now requires the file to be in the file list
* IO_FILE_FIND_BYNAME: added optional argument useful when checking
  that a file does not yet exist
  + bug correction when filelist is empty
* added IO_FILE_PRINT_LIST subroutine (only for debugging)
* added TPTR2FILE structure to allow construction of arrays of
  pointers to files
* use IO_READ_FIELD for some 3D float arrays (in read_field.f90)
* OPEN_ll: added UPDATE_METADATA internal subroutines to treat file metadata

Philippe 27/07/2017: bug corrections: NMODEL is not yet known when calling INI_FIELD_LIST -> use max value
+ NDIMS was wrong for VISI_HOR field (DIAG)

* OPEN_ll: added optional argument TPFILE (used for the moment for IO_ZSPLIT case)
* INI_MODEL_n: add TDIAFILE in file list

* added IO_READ_FIELD_BYNAME_X0/X2/T0 and IO_READ_FIELD_BYFIELD_X0/X2/T0 subroutines
  to IO_READ_FIELD procedure
* added IO_READ_FIELD_LFI_X0/X2/T0 subroutines to IO_READ_FIELD_LFI procedure
* added IO_READ_FIELD_NC4_X0/X2/T0 subroutines to IO_READ_FIELD_NC4 procedure
* use IO_READ_FIELD in SET_GRID

* added IO_READ_FIELD_BYNAME_X1 and IO_READ_FIELD_BYFIELD_X1 subroutines
  to IO_READ_FIELD procedure
* added IO_READ_FIELD_LFI_X1 subroutine to IO_READ_FIELD_LFI procedure
* added IO_READ_FIELD_NC4_X1 subroutine to IO_READ_FIELD_NC4 procedure
* bug corrections in IO_READ_CHECK_FIELD_ATTR_NC4
* use IO_READ_FIELD in INI_MODEL_n

* added IO_READ_FIELD_BYNAME_C0 and IO_READ_FIELD_BYFIELD_C0 subroutines
  to IO_READ_FIELD procedure
* added IO_READ_FIELD_LFI_C0 subroutine to IO_READ_FIELD_LFI procedure
* added IO_READ_FIELD_NC4_C0 subroutine to IO_READ_FIELD_NC4 procedure

* added IO_READ_FIELD_BYNAME_L0 and IO_READ_FIELD_BYFIELD_L0 subroutines
  to IO_READ_FIELD procedure
* added IO_READ_FIELD_LFI_L0 subroutine to IO_READ_FIELD_LFI procedure
* added IO_READ_FIELD_NC4_L0 subroutine to IO_READ_FIELD_NC4 procedure
* small improvements / bug corrections

* added IO_BCAST_FIELD_METADATA subroutine
* added IO_READ_CHECK_FIELD_ATTR_NC4 subroutine
* do not use FMHEADER anymore for IO_READ_FIELD and its subroutines
* treat error messages as soon as possible

* added IO_READ_FIELD_LFI interface
* 1st version of IO_READ_FIELD_LFI_N0 (not yet fully implemented)
* corrected problems in ini_segn if process is not the owner of the file

* added IO_READ_FIELD_NC4 interface
* 1st version of IO_READ_FIELD_NC4_N0 (not yet fully implemented)
* set values of NNCID and NLFIFLU to file read in INI_SEG_n (temporary way of doing it)

* added IO_READ_FIELD interface
* 1st version of IO_READ_FIELD_BYFIELD_N0 (not yet fully implemented)
* restructuration of INI_SEG_n to allow earlier initialization of TFIELDLIST

* IO_WRITE_FIELD_LFI_C0: do not trim character string (size must be the same at read)
* IO_WRITE_FIELD_LFI_T0: use TZFIELD instead of TPFIELD
* IO_WRITE_HEADER: write DAD_NAME with a correct length string (for LFI files)
* NCREADN0, NCREADN1 and NCREADN2: accept NF90_INT1 used when writing booleans