Add the full CMake copyright to FindGLEW.

FindGLEW was copied from CMake 2.8.11 so we need to replace the
partial license text in the file with the full license as provided
by CMake 2.8.11 which is a bsd 3 clause.

We also remove FindGLEW.cmake from the copyright test that we have.
Merge branch 'FindGLEW_copyright'