ITK 4 Update

Extracted from previous PR #30, here is what is useful to switch the superproject to ITK 4, and add some flags needed for Mac changes. To work properly, many branches need to be merged / pull requested: 

- dtk (medinria clone) : branch clang-mavericks (needed for mac)
- QtDCM : https://github.com/medInria/qtdcm/pull/1
- RPI : https://github.com/Inria-Asclepios/RPI/pull/8
- TTK : svn branch itk-4 need to replace trunk
- medInria-public : https://github.com/medInria/medInria-public/pull/112 

PS: you can still use PR #30 to test compilation and run (it allows you to have everything included in the superproject).