patch 7.4.1989

Problem:    filter() and map() only accept a string argument.
Solution:   Implement using a Funcref argument (Yasuhiro Matsumoto, Ken
            Takata)

src/version.c

@@ -758,6 +758,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1989,
 /**/
     1988,
 /**/