patch 9.1.0284: make testclean is not able to delete failed screendumps

Problem:  make testclean is not able to delete failed screendumps.
Solution: Remove the "failed" directory when necessary.
          (Julio B)

Patch 8.1.1080 changed the way that failed screendumps are saved, but
the "rm -rf *.failed" clean command was not ported correctly.

closes: #14468

Signed-off-by: Julio B <julio.bacel@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/testdir/Makefile

@@ -89,7 +89,7 @@ RUN_VIM = VIMRUNTIME=$(SCRIPTSOURCE) $(VALGRIND) $(VIMPROG) -f $(GUI_FLAG) -u un
 # Delete files that may interfere with running tests.  This includes some files
 # that may result from working on the tests, not only from running them.
 clean:
-	-rm -rf *.out *.failed *.res *.rej *.orig XfakeHOME Xdir1 Xfind
+	-rm -rf *.out *.failed *.res *.rej *.orig XfakeHOME Xdir1 Xfind failed
 	-rm -f opt_test.vim test_result.log $(CLEANUP_FILES)
 	-rm -rf $(RM_ON_RUN) $(RM_ON_START)
 	-rm -f valgrind.*

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    284,
 /**/
     283,
 /**/