iFit/isvalid

 Check fields for data_array object

   >> [ok, mess] = isvalid (w)

   ok      ok=true if valid, =false if not
   mess    Message if not a valid object, empty string if is valid.
%   Overloaded methods:
      sqw/isvalid
      testsigvar/isvalid
      sigvar/isvalid
      IX_dataset_3d/isvalid
      IX_dataset_2d/isvalid
      IX_dataset_1d/isvalid
      IX_axis/isvalid
      rundata/isvalid
      IX_sample/isvalid
      IX_moderator/isvalid
      IX_mask/isvalid
      IX_map/isvalid
      IX_fermi_chopper/isvalid
      IX_aperture/isvalid
      spe/isvalid
      slice/isvalid
      phxObject/isvalid
      parObject/isvalid
      cut/isvalid
      sqw/isvalid
      sigvar/isvalid
      d4d/isvalid
      d3d/isvalid
      d2d/isvalid
      d1d/isvalid
      d0d/isvalid
      timer/isvalid
      serial/isvalid
      handle/isvalid
      instrument/isvalid