[X] Include MesaLib conditionally (opengl option)
[X] Declare License in Makefile
[X] Remove MASTER_SITES no longer working
    Snapshots for FLTK 2.0 branch are no longer provided.
    FLTK homepage recommends to use Git.
    => Use Git
[X] FL_MINOR_VERSION is defined to 1
    => Use Version 2.1 for package
    => Patch fltk2-config script to report version 2.1.0
[X] Generate (no longer shipped) configure script via autoconf
    => Add autoconf to USE_TOOLS
[X] Rework patches
    - patch-ac removed
      Git release has no configure script (we generate it via autoconf)
      => patch-ab is therefore sufficient.
    - patch-ad reduced
    - patch-ae removed (now uses DESTDIR out-of-the-box)
    - patch-ag reduced (setjmp() part already merged)
    - patch-ah reduced (the HP-UX and DragonFly mappings are now catched by
      the POSIX check)
    => Rebuild patches and add comments
[X] Update PLIST
    => Add "include/fltk/WidgetAssociation.h"
[X] Remove test target
    => There is no test rule in top level Makefile
