* More memmory link related corrections and documentation fixes.

  * More memmory link related corrections and documentation fixes.
        Notes on valgrind:
          - maximum info is obtained with a command of the form:
            valgrind --leak-check=yes --leak-resolution=high --num-callers=40
                   --show-reachable=yes PrintHeader
          - the remaining reachable blocks seem to come from the STL
            allocation scheme through the usage of map and list. It looks
            like this memory cannot be freed but it is not a memory leak
            (in fact further invocation to the STL would recollect the
             unused memory allthough it cannot explicitely be freed).
      * gdcmPython/demo/vtkGdcmDemo.py added: this is a small demo
        of displaying an image parsed with gdcm and displayed with VTK.
        Note: some images don't seem to work e.g.
            python vtkGdcmDemo.py  ../../Data/US-RGB-8-esopecho.dcm
      * src/gdcmHeader.x: dicom_vr and Dicts are not class members anymore.
        Allthough this weakens the semantics, it is a ditch attempt to
        make gdcm more thread friendly.   --- Frog