In the future, tree.cxx and tree.h should be removed from svn
once tree.fl is merged into to the build system, so that it
generates the .cxx/.h files as part of an fltk build.
git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3@7638 ea41ed52-d2ee-0310-a9c1-e6b18d33e121