patch 8.1.1218: cannot set a directory for a tab page

Problem:    Cannot set a directory for a tab page.
Solution:   Add the tab-local directory. (Yegappan Lakshmanan, closes #4212)
diff --git a/src/proto/ex_docmd.pro b/src/proto/ex_docmd.pro
index 710f48b..9934d60 100644
--- a/src/proto/ex_docmd.pro
+++ b/src/proto/ex_docmd.pro
@@ -37,7 +37,7 @@
 void tabpage_new(void);
 void do_exedit(exarg_T *eap, win_T *old_curwin);
 void free_cd_dir(void);
-void post_chdir(int local);
+void post_chdir(int tablocal, int winlocal);
 void ex_cd(exarg_T *eap);
 void do_sleep(long msec);
 void ex_may_print(exarg_T *eap);