some cosmetic cleanup so that compilation : -W -Wall -Werror can pass.

some cosmetic cleanup so that compilation : -W -Wall -Werror can pass.
1. I have added some unsigned where needed
2. Some function parameter not used -> (void)
3. In gdcmDicomDir.cxx, add GDCM_DICOMDIR_NONE case
4. g++ don't like character '\' in comment
5. #define jpeg_create_decompress  jCreaDecompress this really need to be fixed
6. virtualize destructor of gdcmObject ... leakage
7. sscanf(g->first.c_str(),"%x",&gr_bid); this also really need to be fixed
8. gdcm/src/jpeg/libijg8/CMakeLists.txt, remove compression file (as we only do decompression, right ?)