From Mattias Helsing, "CMake have release 3.0 and 3.1 and we have some bad checks for cmake
major version when settings cmake policies in CMakeLists.txt. This fixes it"


git-svn-id: http://svn.openscenegraph.org/osg/OpenSceneGraph/trunk@14620 16af8721-9629-0410-8352-f15c8da7e697