patch 8.0.0517: there is no way to remove quickfix lists

Problem:    There is no way to remove quickfix lists (for testing).
Solution:   Add the 'f' action to setqflist(). Add tests. (Yegappan
            Lakshmanan)

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    517,
 /**/
     516,
 /**/