Mathieu Marache, he added the last missing piece to this puzzle.
I think it is safe to commit these changes to trunk, as the traditional
way via dylibs should work as before.
Here's some more info how to get frameworks:
With these modifications it is possible to compile frameworks on OS X,
when you set the Cmake-option OSG_COMPILE_FRAMEWORKS to true. If you
want to embed the frameworks in your app-bundle make sure to set
OSG_COMPILE_FRAMEWORKS_INSTALL_NAME_DIR accordingly.
You'll have to build the install-target of the generated xcode-projects
as this sets the install_name_dirs of the frameworks and plugins."
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