APPEND and NCONC

[NGALL@G.BBN.COM]

The doc for APPEND should be clarified to warn the user that APPEND
can return a non-list, e.g.,
(append '() t) => t

Also, the doc for NCONC should be clarified so that NCONC behaves
analogously to APPEND when its last argument is an atom.

-- Nick
{Sorry if this is a repeat.}