Added the Fl_Shaped_Window class to support windows of arbitrary shapes.
The new class is fully Doxygen-documented.
Added an example program (example/shapedwindow.cxx) that exercises the new class.
Modified all IDE-supporting files accordingly.

git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10255 ea41ed52-d2ee-0310-a9c1-e6b18d33e121