h4map

Description:
    - when typed "hmap" without argument, got Segmentation fault
      -> fixed: moved the check for argc to before the other command line check
    - when file name is invalid, nothing happened
      -> fixed: printed informative message that file is not found
    - Added CHECK to many API calls (more to do)
    - added _HDF_DIMENSION, _HDF_UDIMENSION, DIM_VALS, DIM_VALS01 to
      INTERNAL_HDF_CLASSES in function isInternal, also tried to use both
      vgroup and vdata, not just sometime vgroup, sometime vdata.
    - call to some H functions generated compilation errors because of
      "difference in signedness."  Fixed parameter types.
    - prevented a memory leak by adding: ref_count_free(&ris_visited);
    - changed all free, malloc, str... functions to HDfree, HDmalloc, HDstr...
    - added many line comments and function headers