[CMake] color output with GNU Screen

[thewtex]

> There is a test somewhere in cmake where it checks whether it is running in a 
> real terminal which is color-capable (or something like this, I don't know 
> the details).
> 
> Maybe this returns false with GNU screen ?
> Can you have a look ?
> 
> Alex
> 

Thanks for the tip.  Filed the patch here:

http://public.kitware.com/Bug/view.php?id=6833

Fix for GNU Screen and a bunch of other terminals.