updated for version 7.4.312

Problem:    Cannot figure out what argument list is being used for a window.
Solution:   Add the arglistid() function. (Marcin Szamotulski)

src/globals.h

@@ -601,6 +601,7 @@ EXTERN int	mf_dont_release INIT(= FALSE);	/* don't release blocks */
  * to this when the window is using the global argument list.
  */
 EXTERN alist_T	global_alist;	/* global argument list */
+EXTERN int	max_alist_id INIT(= 0);	    /* the previous argument list id */
 EXTERN int	arg_had_last INIT(= FALSE); /* accessed last file in
 					       global_alist */