Prefer files from the CMake module directory when including from there.

Starting with CMake 2.8.4, if a cmake-module shipped with CMake (i.e. located in the CMake module directory) calls include() or find_package(), the files located in the CMake module directory are preferred over the files in CMAKE_MODULE_PATH. This makes sure that the modules belonging to CMake always get those files included which they expect, and against which they were developed and tested. In all other cases, the files found in CMAKE_MODULE_PATH still take precedence over the ones in the CMake module directory. The OLD behavior is to always prefer files from CMAKE_MODULE_PATH over files from the CMake modules directory.

This policy was introduced in CMake version 2.8.4. CMake version 3.0.2 warns when the policy is not set and uses OLD behavior. Use the cmake_policy command to set it to OLD or NEW explicitly.