patch 9.0.0327: items() does not work on a list

Problem:    items() does not work on a list. (Sergey Vlasov)
Solution:   Make items() work on a list. (closes #11013)
diff --git a/src/proto/list.pro b/src/proto/list.pro
index 3f77f04..611aeac 100644
--- a/src/proto/list.pro
+++ b/src/proto/list.pro
@@ -35,6 +35,7 @@
 int list_assign_range(list_T *dest, list_T *src, long idx1_arg, long idx2, int empty_idx2, char_u *op, char_u *varname);
 void f_flatten(typval_T *argvars, typval_T *rettv);
 void f_flattennew(typval_T *argvars, typval_T *rettv);
+void list2items(typval_T *argvars, typval_T *rettv);
 int list_extend(list_T *l1, list_T *l2, listitem_T *bef);
 int list_concat(list_T *l1, list_T *l2, typval_T *tv);
 list_T *list_slice(list_T *ol, long n1, long n2);