Frequently impossible to scroll down while drag-selecting

[homunq]

In controls that touch the bottom of the screen, it is impossible to scroll down while drag-selecting. This is inherited from gtk, but is much more of a problem in sugar, since many controls in sugar are immovably attached to the bottom of the screen.

This affects log, terminal, and other activities. The only reason it does not affect Write/Abiword is but 2169.

If the mouse touches the bottom of the screen during drag-selection, the current control should scroll down if possible. This should be handled by sugar and not on a per-activity basis.

I am creating this bug in sugar, though it also relates to gtk-theme.