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/gui_mac.c b/src/gui_mac.c
index db9f959..6386b63 100644
--- a/src/gui_mac.c
+++ b/src/gui_mac.c
@@ -1105,7 +1105,8 @@
 	}
 
 	/* Change directory to the location of the first file. */
-	if (GARGCOUNT > 0 && vim_chdirfile(alist_name(&GARGLIST[0])) == OK)
+	if (GARGCOUNT > 0
+		      && vim_chdirfile(alist_name(&GARGLIST[0]), "drop") == OK)
 	    shorten_fnames(TRUE);
 
 	goto finished;