How to downgrade *Completions*

[Guangliang Yang]

 Hi,

I am using GNU Emacs 25.0.94.1 (x86_64-redhat-linux-gnu, GTK+ Version
3.20.4) of 2016-05-18.

Everything is good for me except *Completions*.
1. Personally, I don't like its resizing.
2. It is not compatible with ECB. When ECB is available, it will alwasy
show in *minibuffer*.

The following is my ECB structure. A is to show the code, B is to run
temporary buffers, and C is to show the method list. A and B are normal
windows, while C is *dedicated*.


+-----------+----------+
|               |             |
|    A         |             |
|                |            |
|                |     C    |
+-----------+            |
|    B         |             |
|               |             |
+-----------+----------+

Assume I am working in A or B. When I use "C-x C-f", the *Completions* will
be shown in minibuffer.

I read the official manual and also rewrote "display-buffer-function", but
still do not well solve the problem.


So can I just downgrade the *Completions* to emacs24's version?

Regards,
Yang