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_autocmd.vim b/src/testdir/test_autocmd.vim
index e6c7ec0..ca8cc04 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
@@ -70,9 +70,7 @@
   endfunc
 
   func Test_cursorhold_insert_with_timer_interrupt()
-    if !has('job')
-      return
-    endif
+    CheckFeature job
     " Need to move the cursor.
     call feedkeys("ggG", "xt")
 
@@ -535,9 +533,7 @@
 endfunc
 
 func Test_OptionSet()
-  if !has("eval") || !exists("+autochdir")
-    return
-  endif
+  CheckOption autochdir
 
   badd test_autocmd.vim
 
@@ -1778,12 +1774,11 @@
 endfunc
 
 func Test_nocatch_wipe_dummy_buffer()
-  if has('quickfix')
-    " Nasty autocommand: wipe buffer on any event.
-    au * x bwipe
-    call assert_fails('lv½ /x', 'E937')
-    au!
-  endif
+  CheckFeature quickfix
+  " Nasty autocommand: wipe buffer on any event.
+  au * x bwipe
+  call assert_fails('lv½ /x', 'E937')
+  au!
 endfunc
 
 function s:Before_test_dirchanged()
@@ -1834,9 +1829,7 @@
 endfunc
 
 function Test_dirchanged_auto()
-  if !exists('+autochdir')
-    return
-  endif
+  CheckOption autochdir
   call s:Before_test_dirchanged()
   call test_autochdir()
   autocmd test_dirchanged DirChanged auto call add(s:li, "auto:")
@@ -2087,9 +2080,8 @@
 " - FileReadPost	decompress the file
 func Test_ReadWrite_Autocmds()
   " Run this test only on Unix-like systems and if gzip is available
-  if !has('unix') || !executable("gzip")
-    return
-  endif
+  CheckUnix
+  CheckExecutable gzip
 
   " Make $GZIP empty, "-v" would cause trouble.
   let $GZIP = ""