* src/gdcmDicSet.[h|cxx] : add virtual entries to have a reference of

 * src/gdcmDicSet.[h|cxx] : add virtual entries to have a reference of
       entries created while parsing the header. Thus, they will be destroyed
       when the gdcmDictSet will be destroyed
     * src/gdcmHeader.cxx, gdcmHeaderEntrySet.cxx : uses virtual entries of
       gdcmDictSet
     -- BeNours