bug#14843: 24.3.50; `line-move', `line-move-visual' need doc strings

[Drew Adams]

> > Perhaps it is also a small wonder that NONE of the uses of `line-move',
> > including those in simple.el itself, make ANY USE of the additional
> > parameters introduced in Emacs 22 (and not used even in 22).
> 
> That's not true.  These arguments are used by next-line and previous
> line.

Yes and no.  One of them is used; the other (TO-END) is not.

But you're missing the point.  Neither is used in any of the zillion uses
of `line-move' - other than `(next|previous)-line'.  And that lends some
support to the idea that those programming those uses might not have even
understood these undocumented parameters.

In addition, it is NOT the case that optional parameter TO-END is used
anywhere.  And I do mean strictly anywhere this time.  It was introduced
in Emacs 22 but NEVER used anywhere, AFAICT.  Again, not being documented
might be one reason this vestige (vestige of nothing) has never been
used and has never been removed.

I made this clear in bug #14844 (where I mentioned only TO-END, not also
TRY-VSCROLL).