Fix building with -fno-implicit-templates.

http://bugs.gentoo.org/show_bug.cgi?id=90819

Patch by Mike Frysinger (C++ sucks btw)

--- c++/demo.cc
+++ c++/demo.cc
@@ -152,6 +152,8 @@
     return FALSE;
   }
 };
+template class MyAction<UserData>;
+template class NCURSES_IMPEXP NCursesUserItem<UserData>;
 
 class QuitItem : public NCursesMenuItem
 {