Implement scrollbars

- They work almost as you'd expect, though holding the mouse down on an arrow only scrolls once, and it's a little jerky
- Add an additional refresh option to redraw_screen, currently only partially implemented
- Scrollbars now have a page size in addition to pos and max
- cControl::handleClick() now takes the location clicked as a parameter, though the default implementation doesn't use it
- cControl::handleClick() is no longer responsible for redrawing the control when there is no parent dialog
- Fix cTextMsg not allowing retrieval of frame style

osx/dialogxml/control.h

@@ -98,7 +98,7 @@ public:
 	virtual void setColour(sf::Color clr) throw(xUnsupportedProp) = 0;
 	virtual sf::Color getColour() throw(xUnsupportedProp) = 0;
 	virtual bool isClickable() = 0;
-	virtual bool handleClick();
+	virtual bool handleClick(location where);
 	cControl(eControlType t, sf::RenderWindow& p);
 	cControl(eControlType t, cDialog& p);
 	virtual ~cControl();