patch 8.1.1138: plugins don't get notified when the popup menu changes

Problem:    Plugins don't get notified when the popup menu changes.
Solution:   Add the CompleteChanged event. (Andy Massimino. closes #4176)
diff --git a/src/proto/popupmnu.pro b/src/proto/popupmnu.pro
index e2ae92a..c019663 100644
--- a/src/proto/popupmnu.pro
+++ b/src/proto/popupmnu.pro
@@ -8,6 +8,7 @@
 int pum_visible(void);
 void pum_may_redraw(void);
 int pum_get_height(void);
+void pum_set_event_info(dict_T *dict);
 int split_message(char_u *mesg, pumitem_T **array);
 void ui_remove_balloon(void);
 void ui_post_balloon(char_u *mesg, list_T *list);