bug#12419: Mouse click changes layout

[Drew Adams]

>   ------------
> |            |
> |            |
>   ------------
> |            |
> |            |
>   ------------
> |            |
> |            |
>   ------------
> 
> you drag the lower divider up you first get
> 
>   ------------
> |            |
> |            |
>   ------------
> |            |
>   ------------
> |            |
> |            |
> |            |
>   ------------
> 
> and then
> 
>   ------------
> |            |
>   ------------
> |            |
>   ------------
> |            |
> |            |
> |            |
> |            |
>   ------------

AFAICT, in previous releases, the second change does not occur. Only the first
one does.

> because the idea is that you want to show more in the bottom window.
> When you now drag the same divider back you get
> 
>   ------------
> |            |
>   ------------
> |            |
> |            |
>   ------------
> |            |
> |            |
> |            |
>   ------------
> 
> because the idea is to show more of the middle window and then
> 
>   ------------
> |            |
>   ------------
> |            |
> |            |
> |            |
>   ------------
> |            |
> |            |
>   ------------
> 
> which is not the initial configuration.

AFAICT, in previous releases you get exactly the opposite changes from when you
dragged the divider up: only the middle window is affected in both cases.

That is pretty consistent.  Whether it is generally better or not, I don't know.
But perhap it should be a user choice (option), in case some users prefer the
traditional behavior.