patch 8.1.1476: no statistics displayed after running tests

Problem:    No statistics displayed after running tests.
Solution:   Summarize the test results. (Christian Brabandt, closes #4391)
            Also make it possible to report a skipped file.
diff --git a/src/testdir/test_autochdir.vim b/src/testdir/test_autochdir.vim
index 90538fb..1f99858 100644
--- a/src/testdir/test_autochdir.vim
+++ b/src/testdir/test_autochdir.vim
@@ -1,7 +1,7 @@
 " Test 'autochdir' behavior
 
 if !exists("+autochdir")
-  finish
+  throw 'Skipped: autochdir feature missing'
 endif
 
 func Test_set_filename()