bug#3022: 23.0.92; triangle images in Customize buffers are just plain bad

[Chong Yidong]

> While the idea behind the triangles (arrows) in Customize is good
> (actually, I believe it was I who suggested it), the current effect is
> quite bad.
>
> If the value is shown, then the triangle points downward. Typically,
> that symbol means that clicking it will display something additional
> below the symbol. Instead, the value disappears.
>
> If the value is not shown, the the symbol is a right-pointing
> triangle. That's OK in this case, since it suggests that clicking it
> will display something to the right, and the value is to the right.
>
> However, for the symbol that replaces `More', a right-pointing
> triangle is inappropriate, since the text is not displayed to its
> right, but below it.

This is a very standard user interface idiom, known as "disclosure
triangles".