patch 9.0.1007: there is no way to get a list of swap file names

Problem:    There is no way to get a list of swap file names.
Solution:   Add the swapfilelist() function.  Use it in the test script to
            clean up.  Remove deleting individual swap files.

src/main.c

@@ -507,7 +507,7 @@ vim_main2(void)
      */
     if (recoverymode && params.fname == NULL)
     {
-	recover_names(NULL, TRUE, 0, NULL);
+	recover_names(NULL, TRUE, NULL, 0, NULL);
 	mch_exit(0);
     }