patch 8.1.1826: tests use hand coded feature and option checks

Problem:    Tests use hand coded feature and option checks.
Solution:   Use the commands from check.vim in more tests.
diff --git a/src/testdir/test_autochdir.vim b/src/testdir/test_autochdir.vim
index 1f99858..98d1af7 100644
--- a/src/testdir/test_autochdir.vim
+++ b/src/testdir/test_autochdir.vim
@@ -1,8 +1,7 @@
 " Test 'autochdir' behavior
 
-if !exists("+autochdir")
-  throw 'Skipped: autochdir feature missing'
-endif
+source check.vim
+CheckOption autochdir
 
 func Test_set_filename()
   let cwd = getcwd()