[CMake] FLTK issue with cmake

[John Drescher]

>> Can i use qt instead of fltk?
>
> That is highly recommended. Qt is used by a significantly larger user
> base and is developed and tested more thoroughly. On top of that many
> of the Kitware applications like paraview are Qt based. Although it
> will not help you run the FLTK examples..

BTW. If you move to Qt. Make sure you build Qt-4.8.X with the compiler
you will use for ITK, VTK ...

Do not try to use Qt 5.X yet.

John