patch 8.0.1445: cannot act on edits in the command line

Problem:    Cannot act on edits in the command line.
Solution:   Add the CmdlineChanged autocommand event. (xtal8, closes #2603,
            closes #2524)
diff --git a/src/testdir/test_autocmd.vim b/src/testdir/test_autocmd.vim
index d8fddff..b7d43b5 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
@@ -812,6 +812,18 @@
 endfunc
 
 func Test_Cmdline()
+  au! CmdlineChanged : let g:text = getcmdline()
+  let g:text = 0
+  call feedkeys(":echom 'hello'\<CR>", 'xt')
+  call assert_equal("echom 'hello'", g:text)
+  au! CmdlineChanged
+
+  au! CmdlineChanged : let g:entered = expand('<afile>')
+  let g:entered = 0
+  call feedkeys(":echom 'hello'\<CR>", 'xt')
+  call assert_equal(':', g:entered)
+  au! CmdlineChanged
+
   au! CmdlineEnter : let g:entered = expand('<afile>')
   au! CmdlineLeave : let g:left = expand('<afile>')
   let g:entered = 0