Add unittests to demo program menu.

This test program may not be in the optimal position in the menu,
but w/o restructuring more of the menu this was the best position
I could find. Maybe we can restructure the menu in the future.


git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10433 ea41ed52-d2ee-0310-a9c1-e6b18d33e121