cppbind: Make Mac and Windows happy and add forward declaration

simgear/nasal/cppbind/cppbind_fwd.hxx

@@ -22,6 +22,7 @@
 
 #include <simgear/nasal/nasal.h>
 #include <cstddef>
+#include <string>
 
 namespace nasal
 {
@@ -30,7 +31,7 @@ namespace nasal
   class Context;
   class ContextWrapper;
   class Hash;
-  class Me;
+  struct Me;
   class Object;
   class String;
 
@@ -49,6 +50,9 @@ namespace nasal
   template<class Var>
   struct from_nasal_ptr;
 
+  template<class T>
+  T get_member(naContext c, naRef obj, const std::string& name);
+
 } // namespace nasal
 
 #endif /* SG_NASAL_CPPBIND_FWD_HXX_ */