patch 8.2.1432: various inconsistencies in test files

Problem:    Various inconsistencies in test files.
Solution:   Add modelines where they were missing.  Use Check commands instead
            of silently skipping over tests.  Adjust indents and comments.
            (Ken Takata, closes #6695)
diff --git a/src/testdir/test_changelist.vim b/src/testdir/test_changelist.vim
index 3741f32..9b28ede 100644
--- a/src/testdir/test_changelist.vim
+++ b/src/testdir/test_changelist.vim
@@ -1,10 +1,10 @@
 " Tests for the changelist functionality
 
+source check.vim
+
 " Tests for the getchangelist() function
 func Test_getchangelist()
-  if !has("jumplist")
-    return
-  endif
+  CheckFeature jumplist
 
   bwipe!
   enew