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>
diff --git a/src/testdir/Makefile b/src/testdir/Makefile
index fd2e56c..4e476f9 100644
--- a/src/testdir/Makefile
+++ b/src/testdir/Makefile
@@ -89,7 +89,7 @@
 # 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.*
diff --git a/src/version.c b/src/version.c
index dc9f775..bafbe5b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    284,
+/**/
     283,
 /**/
     282,