bug#12922: 24.3.50; `make-pointer-invisible' don't seem to work

[Drew Adams]

> a bug in the documentation, i.e., the program's behavior is
> the intended one, but the documentation doesn't
> describes that behavior.  And that is what happens here.
> 
> Definitions aside, the fact is that currently, any user of the
> MS-Windows port of Emacs will be confused when she reads about the
> `make-pointer-invisible' variable and notice that the actual behavior
> of the program does not match the documentation.

If it is not possible to update the doc wrt specific platforms here and there,
describing specific limitations per platform, perhaps it would at least be
possible in some cases (like this one) to state that the feature (whatever it is
- making the pointer invisible, for instance) "might not be available on some
platforms".

That would at least give readers a heads-up, so they do not completely wonder
what's going on and whether (a) there is perhaps a product bug or (b) they are
perhaps misreading the doc.

Yes, such a weak caveat is true for nearly all features.  But this is not
something black-and-white, all-or-nothing.

If such caveats are used judiciously, i.e., only in places where we in fact do
not support a feature on some platform (especially a commonly used platform) and
where we realize there might well be a chance for reader confusion, then I, for
one, think they could be helpful.