bug#34478: DocView uses unlisted buffers nobody can get back to

[積丹尼 Dan Jacobson]

We are viewing a document in DocView,
in fact a PDF attachment to a gnus email message.

The problem is, often we wish to switch to other buffers to do other
things, and come back to DocView to finish reading --- back and forth.

But apparently the DocView designers assumed people would just read
short tweets with it, not longer PDFs.

So they use a buffer name *mm*-12345... that
1) does not appear in (C-x C-b) list-buffers.
2) does not get TAB completion when trying to type in

The result is there is no way to find the document you were just
reading, if you dared let it get off the screen by choosing some other
buffer(s).

The only way to continue reading is to go back to the gnus Article
buffer again, and hit RET on the attachment again, and scroll down again
to where you hopefully thought you were!