bug#38457: 27.0.50; dabbrev-expand regression due to message change

[Juri Linkov]

>> I think leaving "M-x" (or any other prompt) unobscured in this
>> situation is a nice benefit, and if it simplifies the code, it's even
>> more desirable.
>
> Implemented in a new patch.

This patch now makes easy to implement message stacking that solves the
issue of several successive calls to message resulting in the user only
seeing the last message.  This problem was raised many times, and now
with a function consisting of 12 lines of code attached below, such
messages are never lost anymore.

It's eyebrow-raising how many messages were missed before.
For example, on startup now it shows 3 lines of messages
I've never seen before:

  Desktop: 1 frame, 19 buffers restored.
  15.095076566 seconds
  Package cl is deprecated

I've only seen the last message "Package cl is deprecated" sometimes
when it was not overwritten by another later message.
Now all accumulated messages are displayed together.

It also allows noticing error messages never seen before.
In Gnus it now shows these lines together, not only the last message:

  Error while decoding: (args-out-of-range  *temp*-306008 1 4346)
  Error while decoding: (args-out-of-range  *temp* 1 7357)
  Fontifying...done

This code depends on the previous patch:

messages-stack.el
Description: application/emacs-lisp