bug#3653: 23.1.50; Gnus/Ido: Saving message's attachment adds filename twice when user hits C-x C-f

In Gnus there's a small bug in saving attached files while ido-mode and
ido-everywhere are active.

When saving an attachment Gnus prompts for a filename, and because
ido-everywhere is turned on ido is also active in the file-saving
prompt. In ido prompt there's command C-x C-f for turning ido off from
that prompt; it falls to the Emacs's default filename prompt. The
problem is that the filename appears now twice in the prompt, like
"~/filename.txtfilename.txt".

Here's the same thing explained in simple steps:

 1. Start Emacs and turn on ido-mode and ido-everywhere:

        C-u M-x ido-mode RET
        C-u M-x ido-everywhere RET

 2. Start Gnus and open a message which has an attachment. There's a
    simple text file attached to this bug report message so you can use
    this message.

 3. When the message is visible move the point the the attachment line

        [2. text/plain; test-attachment.txt]...

    and press "o" (gnus-mime-save-part). Ido-mode's completion-capable
    file-saving prompt should be now active.

 4. Press immediately C-x C-f to go back to the normal save prompt.

 5. You should see path and filename like this in the prompt:

        ~/test-attachment.txttest-attachment.txt

    Obviously the expected result would be

        ~/test-attachment.txt


---------------
In GNU Emacs 23.1.50.5 (i686-pc-linux-gnu, GTK+ Version 2.12.12)
 of 2009-06-23 on mithlond
Windowing system distributor `The X.Org Foundation', version 11.0.10402000
configured using `configure  '--prefix=/home/dtw/local''

Incredibly useful content here.