Clean up header dependencies in the vncviewer directory
diff --git a/vncviewer/Viewport.cxx b/vncviewer/Viewport.cxx
index 733e4a2..d784a42 100644
--- a/vncviewer/Viewport.cxx
+++ b/vncviewer/Viewport.cxx
@@ -52,6 +52,9 @@
 #include <FL/fl_draw.H>
 #include <FL/fl_ask.H>
 
+#include <FL/Fl_Menu.H>
+#include <FL/Fl_Menu_Button.H>
+
 #ifdef WIN32
 #include "win32.h"
 #endif