Typo fixed

[Robert W. Kerns <RWK at SCRC-TENEX>]

    Date: 17 March 1982 01:08-EST
    From: Kent M. Pitman <kmp at MIT-AI>
    In System 79.26, ZMail 40.7, ... microcode 849, ... on Lisp Machine Twenty-two:

    In Kill or Save Buffers (on editor menu), the mouse documentation has
    an apparent typo. For most places the mouse can be on menu, it says:

       Any button an a box to complement its state
Someone seems to have fixed this typo in the source.
(In (:method :basic-multiple-choice :who-line-documentation-string)).