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/scrollbar.h

@@ -12,14 +12,24 @@
 #include "control.h"
 
 class cScrollbar : public cControl {
-	int pos, max;
+	int pos, max, pgsz;
+	enum {
+		PART_UP,
+		PART_PGUP,
+		PART_THUMB,
+		PART_PGDN,
+		PART_DOWN,
+	} pressedPart;
 	click_callback_t onClick;
+	static sf::Texture scroll_gw;
 public:
+	static void init();
 	explicit cScrollbar(sf::RenderWindow& parent);
 	explicit cScrollbar(cDialog& parent);
 	void attachClickHandler(click_callback_t f) throw(xHandlerNotSupported);
 	void attachFocusHandler(focus_callback_t f) throw(xHandlerNotSupported);
 	bool triggerClickHandler(cDialog& me, std::string id, eKeyMod mods, location where);
+	bool handleClick(location where);
 	void setFormat(eFormat prop, short val) throw(xUnsupportedProp);
 	short getFormat(eFormat prop) throw(xUnsupportedProp);
 	void setColour(sf::Color clr) throw(xUnsupportedProp);
@@ -27,8 +37,10 @@ public:
 	bool isClickable();
 	long getPosition();
 	long getMaximum();
+	long getPageSize();
 	void setPosition(long to);
 	void setMaximum(long to);
+	void setPageSize(long to);
 	void draw();
 };