Make select tool react on mouse up rather than mouse down.

[corranwebster]

This is a more natural user interaction, and allows the selection tool to co-exist with other tools (eg. PanTool2) in a nicer fashion.

[cfarrow]

I agree with the change, but I think it should be done in a backwards-compatible way. This change will cause all subclasses of SelectTool that overload normal_left_down to react on mouse down and mouse up. I recommend adding a flag that allows one to modify the selection behavior, and which defaults to the left-down behavior.

[itziakos]

I would also like to note that activating the Tool at mouse_up without marking the position of the mouse_down can cause unexpected behaviour since the mouse_down -> mouse_up can take place far apart from each other.