Update of ropp_pp_spectra_tool to let it handle GRAS raw sampling data

[kmk]

Currently ropp_pp_spectra_tool does not work with GRAS raw sampling data. It doesn not handle navigation bits and datagaps and so output is not useful.Attached is a pretty extensive recoding of ropp_pp_spectra_tool to make it work with GRAS raw sampling data. Essentially I did it by lifting code from ropp_pp_preprocess into ropp_pp_spectra_tool so I think it should be pretty solid. Changes are only to this one routine.

[kmk]

Suggested modified version of ropp_pp_spectra_tool

[Ian Culverwell]

Incorporated at ROPP7.0. Needed to change

  IF (ro_data%Lev1a%Npoints .lt. 100) THEN
    CALL message(msg_warn, "Error: Too few data")
    config%obs_ok = .FALSE.
    RETURN
  ENDIF 

in the MAIN program to the legal f90 statement

      IF (ro_data%Lev1a%Npoints .lt. 100) THEN
        config%obs_ok = .FALSE.
        CALL message(msg_fatal, "Error: Too few data")
      ENDIF 

Tests out OK, but then the test of ropp_pp_spectra_tool in t_ropp_pp.sh uses COSMIC data, so doesn't touch the new code. I think this is probably OK, because we're unlikely to be using this format for RS data much longer anyway (superseded by the nc4 'grouped' data from EUMETSAT). Close ticket for now.