Philippe 02/12/2016: IO:

* added module MODE_READWRITE_LFI
* added interface IO_WRITE_FIELD_LFI inside MODE_READWRITE_LFI
* added IO_WRITE_FIELD_LFI_X2, IO_WRITE_FIELD_LFI_X3
  and IO_WRITE_FIELD_LFI_N0 subroutines to IO_WRITE_FIELD_LFI
* replaced IO calls to use IO_WRITE_FIELD_LFI/NC4 subroutines
  in the IO_WRITE_FIELD_xx subroutines
* added IO_WRITE_FIELD_NC4_X2
* bug correction for IO_WRITE_HEADER_NC4: only the owner of
  the file writes it