listp docstring.

[Luc Teirlinck <teirllm@dms.auburn.edu>]

I do not exactly want to start another thread of the car/cdr type.
But the docstring of listp _really_ can be unclear _even_ for people
who know Lisp.  The current docstring is:

Return t if object is a list.  This includes nil.

But "list" is ambiguous: its strict meaning, intended here, is
"cons cell or nil".  But it is very often used informally in the sense
of "true list", including in some other docstrings.  The car/cdr
thread has shown that there really is some potential confusion here,
since many people do understand list as "true list".

What about the following docstring, which I can install if desired:

Return t if OBJECT is a list, that is, a cons cell or nil.
Otherwise, return nil.

Sincerely,

Luc.