patch 8.0.1649: no completion for argument list commands

Problem:    No completion for argument list commands.
Solution:   Add arglist completion. (Yegappan Lakshmanan, closes #2706)
diff --git a/src/ex_getln.c b/src/ex_getln.c
index 6119ad2..48cccf1 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -4989,6 +4989,7 @@
 #endif
 	    {EXPAND_ENV_VARS, get_env_name, TRUE, TRUE},
 	    {EXPAND_USER, get_users, TRUE, FALSE},
+	    {EXPAND_ARGLIST, get_arglist_name, TRUE, FALSE},
 	};
 	int	i;