Using the two pages:
I have created two folders: build249 and build300. In each I have build the 2 versions. The idea of doing this was to have two versions and just change a line in my CMakeLists.txt file, for switching between the versions:
find_package(OpenCV 2.4.9)
or
find_package(OpenCV 3.0.0)
This way I can test the 3.0.0 beta version and see the differences.
My problem is that when I have changed back to 2.4.9, it cannot find anymore the opencv_nonfree, so I am asking may I have the two versions of OpenCV in paralel and switch between them when I want?