1. An option is included in
        Geo/CGNSOptions.h
   The Entry is
        bool structuredMesh;  // = 1 if structured mesh, = 0 if un-structured mesh

2. The above entry is incorporated in GUI option window - Corresponding code change made in file
        Fltk/fileDialogs.cpp

3. Few subroutines and the actual code that write structured mesh in CGNS format is included in file
        Geo/GModelIO_CGNS.cpp

'ctest' was run - the result was same for both with and without this changes. 01-Nov-2018