patch 8.1.2311: warning for missing function prototype

Problem:    Warning for missing function prototype.
Solution:   Add the proto. (Dominique Pelle, closes #5233)

Author: brammool

src/proto/popupwin.pro

@@ -7,6 +7,7 @@ void popup_set_firstline(win_T *wp);
 int popup_is_in_scrollbar(win_T *wp, int row, int col);
 void popup_handle_scrollbar_click(win_T *wp, int row, int col);
 int popup_top_extra(win_T *wp);
+int popup_left_extra(win_T *wp);
 int popup_height(win_T *wp);
 int popup_width(win_T *wp);
 int popup_extra_width(win_T *wp);

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2311,
 /**/
     2310,
 /**/