Codechange: be consistent in naming the paint function Paint()

Also move this function to be a class member. This to allow
further deduplicating of code in a later commit.

src/video/allegro_v.h

@@ -35,6 +35,7 @@ public:
 
 protected:
 	void InputLoop() override;
+	void Paint() override;
 };
 
 /** Factory for the allegro video driver. */