OS X: Make sure RPATHs are unique to avoid possible corruption.

When using link_directories() and including CMAKE_CFG_INTDIR,
one can end up with duplicate RPATHs in the binary which
install_name_tool cannot fix without corrupting the binary.
Also, the cmake_install.cmake file has been fixed to correctly
handle these generator specific variables.
Merge topic 'osx-rpath-unique' into next

028a5285 OS X: Make sure RPATHs are unique to avoid possible corruption.