BACKENDS: Add PaletteManager interface as comments to GraphicsManager.

This should be a little more comfortable about finding out what's needed to
implement a new graphics manager.

backends/graphics/graphics.h

@@ -84,6 +84,10 @@ public:
 	virtual void setCursorPalette(const byte *colors, uint start, uint num) = 0;
 
 	virtual void displayMessageOnOSD(const char *msg) {}
+
+	// Graphics::PaletteManager interface
+	//virtual void setPalette(const byte *colors, uint start, uint num) = 0;
+	//virtual void grabPalette(byte *colors, uint start, uint num) = 0;
 };
 
 #endif