Re: supporting old Emacs or XEmacs versions

[Richard Stallman]

    In the particular case of lselect.el, given that it has been around
    for for 12+ years and nobody has complained that it does not work,
    it's doubtful that it would be useful.

That is a persuasive argument, so let's mark it as obsolete
in the trunk.

(Though extent-buffer is easy to add in lucid.el.)