Stop abusing InputHandler class for write class

The handler is for incoming data and we should not be abusing that
class for the writer class. Do proper write prototypes for the
relevant functions.
diff --git a/vncviewer/Viewport.h b/vncviewer/Viewport.h
index 3895fc7..536fbb2 100644
--- a/vncviewer/Viewport.h
+++ b/vncviewer/Viewport.h
@@ -22,6 +22,8 @@
 
 #include <map>
 
+#include <rfb/Rect.h>
+
 #include <FL/Fl_Widget.H>
 
 class Fl_Menu_Button;