patch 8.0.1459: cannot handle change of directory

Problem:    Cannot handle change of directory.
Solution:   Add the DirChanged autocommand event. (Andy Massimino,
            closes #888)  Avoid changing directory for 'autochdir' too often.
diff --git a/src/os_win32.c b/src/os_win32.c
index d356c7e..a42df6f 100644
--- a/src/os_win32.c
+++ b/src/os_win32.c
@@ -7193,7 +7193,7 @@
     {
 	do_cmdline_cmd((char_u *)":rewind");
 	if (GARGCOUNT == 1 && used_file_full_path)
-	    (void)vim_chdirfile(alist_name(&GARGLIST[0]));
+	    (void)vim_chdirfile(alist_name(&GARGLIST[0]), "drop");
     }
 
     set_alist_count();