patch 8.0.1587: inserting from the clipboard doesn't work literally

Problem:    inserting from the clipboard doesn't work literally
Solution:   When pasting from the * or + register always assume literally.

src/testdir/test_paste.vim

@@ -1,4 +1,4 @@
-" Tests for bracketed paste.
+" Tests for bracketed paste and other forms of pasting.
 
 " Bracketed paste only works with "xterm".  Not in GUI.
 if has('gui_running')
@@ -66,6 +66,17 @@ func Test_paste_insert_mode()
   bwipe!
 endfunc
 
+func Test_paste_clipboard()
+  if !has('clipboard')
+    return
+  endif
+  let @+ = "nasty\<Esc>:!ls\<CR>command"
+  new
+  exe "normal i\<C-R>+\<Esc>"
+  call assert_equal("nasty\<Esc>:!ls\<CR>command", getline(1))
+  bwipe!
+endfunc
+
 func Test_paste_cmdline()
   call feedkeys(":a\<Esc>[200~foo\<CR>bar\<Esc>[201~b\<Home>\"\<CR>", 'xt')
   call assert_equal("\"afoo\<CR>barb", getreg(':'))