Prevent duplicate mouse up events from ruining mouse input.

This was reproduced by double clicking a xfiledialog. The second click causes it to disappear and GLFW gives us a mouse up with no corresponding mouse down. Maybe because it is a modal child of the GLFW window? Hope there is no way to get incorrect mouse downs, or we'll be screwed.
Merge remote-tracking branch 'origin/master'
Better x,y,width,height.
Merge remote-tracking branch 'origin/master'