From Laurens Voerman, "I made some changes to the top level CMakeLists.txt that might be usefull to other visualstudio users.
1> Disable project grouping for VCExpress users:  the version I proposed previously in
     Re: [osg-submissions] Cmake patch to support folders in IDE (29 Feb 2012)

2> Remove FIND_PACKAGE(OpenAL): not used in any project

3> add /wd4250 for Visual Studio 2012:
     suppress the errors caused by a microsoft fix for a bugfix.
     ref: "Warning messages VS2012..." on osg-users (30 May 2012)
"