Change SelectionListener interface so it receives the set of lines added and removed from selection, instead of just the complete new selection.
Update VisualTool<> to use SelectionListener to receive selection change notifications.
This change (temporarily, I hope) breaks feature selection in visual drag mode, when changing selection via the grid. This is caused by the grid selection change first clearing the entire selection, which sends a separate notification about selection clear. This causes the last visual feature to be deselected, and then the visual tool base reselects the active line, causing a new notification for selection to be sent. The active line happens to be the newly clicked line, and the selection notification enters during the externalChange guard being set, and is then ignored for feature update purposes. When control returns to the original SelectRow call in the grid, the line to be selected has already been selected and then nothing happens.
The best fix is to avoid two notifications being required to deselect all then reselect one line in the first place, so making the grid selection handling saner is the best fix.
Originally committed to SVN as r4602.
