add Yap_FileDescriptorFromStream at request from NF.

C/c_interface.c

@@ -511,6 +511,7 @@ X_API int      STD_PROTO(YAP_CloseList,(Term, Term));
 X_API int      STD_PROTO(YAP_IsAttVar,(Term));
 X_API Term     STD_PROTO(YAP_AttsOfVar,(Term));
 X_API Term     STD_PROTO(YAP_TermHash,(Term));
+X_API void    *STD_PROTO(YAP_FileDescriptorFromStream,(Term));
 
 static int (*do_getf)(void);
 
@@ -2531,3 +2532,13 @@ YAP_TermHash(Term t)
   return attv->Atts;
 }
 
+X_API void *
+YAP_FileDescriptorFromStream(Term t)
+{
+ 
+  t = Deref(t);
+  if (IsVarTerm(t))
+    return NULL;
+  return Yap_FileDescriptorFromStream(t);
+}
+