extendable selection
extendable selection

I'm now merging this with master so it gets some testing. Known issues: SelectionRatio missing, missing pointers, shouldn't mask the image borders on selection

mono/f-spot,mans0954/f-spot,nathansamson/F-Spot-Album-Exporter,dkoeb/f-spot,Yetangitu/f-spot,dkoeb/f-spot,nathansamson/F-Spot-Album-Exporter,Yetangitu/f-spot,mans0954/f-spot,mono/f-spot,Sanva/f-spot,GNOME/f-spot,GNOME/f-spot,Sanva/f-spot,Yetangitu/f-spot,mono/f-spot,NguyenMatthieu/f-spot,Sanva/f-spot,dkoeb/f-spot,dkoeb/f-spot,dkoeb/f-spot,mono/f-spot,NguyenMatthieu/f-spot,Yetangitu/f-spot,Sanva/f-spot,nathansamson/F-Spot-Album-Exporter,mans0954/f-spot,mono/f-spot,nathansamson/F-Spot-Album-Exporter,NguyenMatthieu/f-spot,GNOME/f-spot,NguyenMatthieu/f-spot,GNOME/f-spot,mans0954/f-spot,mans0954/f-spot,GNOME/f-spot,mans0954/f-spot,dkoeb/f-spot,NguyenMatthieu/f-spot,Yetangitu/f-spot,Sanva/f-spot,mono/f-spot