[CMake] How to use CMAKE_POLICY?

[Alexander Neundorf]

On Monday 17 December 2012, David Cole wrote:
> If you need to set a policy to OLD, then we have failed...
> 
> Why do you need to set a policy to OLD?

To get the old behaviour, and to silence warnings, which could lead developers 
to change the cmake code and switch to the NEW behaviour, I think.

Alex