The reasons for that are twofold:

1) LINK_PRIVATE is only available since CMake 2.8.7.
2) The way it was used generated a warning because of CMake policy CMP0023:

   http://www.cmake.org/cmake/help/v2.8.12/cmake.html#policy:CMP0023

Using LINK_INTERFACE_LIBRARIES actually causes another warning - this time
because of CMake policy CMP0022:

   http://www.cmake.org/cmake/help/v2.8.12/cmake.html#policy:CMP0022

I set the policy to OLD, because NEW means subtle changes when compiling
with CMake 2.8.12, and I don't want to research that this close to release.
:-)

I also removed the setting of CMP0003, because it's set by
cmake_minimal_version anyway.

It was actually acting as an additional argument, breaking the error message.

Linker dependencies to all OpenCV modules are invalid.
We should not include other bindings in this list (like "opencv_python").

Removed incorrect release of obtained colorspace. This fixes bug #3318 (updated commit for 2.4 branch)

Bug report and inspiration: http://code.opencv.org/issues/3328