This commit adds the basic setup in CMake to allow SDL as a base
library for FLTK on OS X (and probably for other platforms as well).
The SDL library driver set is derived from yet another new driver
set named 'Pico'. 'Pico' is a base class for a driver that will
allow porting of FLTK with the tinyest amount of effort. This
implementation of the SDL driver shall be documented very well
to explain the porting process.
git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3-porting@11262 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
