bug#11934: 24.1; provide variable for pp.el to control max display width

[Drew Adams]

> Well, pp isn't really designed for handling code.

Maybe you mean that it doesn't do a good enough job
of it?  I think it is designed for handling code, as much
as for handling data.  It just doesn't handle them differently.

Lisp code and Lisp data structures are not very different,
though yes, we generally follow some code-specific formatting
conventions - and pp.el does not bother with those (as it
cannot know whether you want to consider the sexp as code
or data).

> I pp'd a function at random...  it may be pretty, but it
> sure is unusual for code...

It's pretty-printed.  And not too bad.

> So I don't really think that's a consideration here.

If you mean that pp.el shouldn't bother to do something
special for code then I agree.  At least until/unless
we add an optional arg to indicate the intention to
interpret the result as code and not data.