* src/gdcmDocEntry.cxx : remove the copy of the DictEntry... there isn't

   * src/gdcmDocEntry.cxx : remove the copy of the DictEntry... there isn't
     correct to copy it. The DictEntry is specified at the DocEntry creation,
     then, it musn't change in the time.
   * src/gdcmDocEntryArchive.[h|cxx] : new class. It's goal is to change the
     header correctly. At this time, the change is only made for the first
     level of the Document. In the future, it might consider sequences.
     The change is made by replacing a DocEntry by an other that is created
     outside the class. The old value is kept. When we restore the header
     status, the added DocEntry is deleted and replaced by the old value.
   * src/gdcmElementSet.h : Set the DocEntryArchive like friend.
   * src/gdcmFile.[h|cxx] : Use the gdcmDocEntryArchive. Add methods to
     set the write type to explicit VR, implicit VR or ACR. Add methods to set
     the write mode to native, decompressed or RGB (but not used at this time)
   -- BeNours