bug#24523: Base64 images makes Emacs slow

[Eli Zaretskii]

merge 24523 13675
thanks

> Date: Sat, 24 Sep 2016 11:09:01 +0200
> From: Andreas Nilsson <an@bahnhof.se>
> Cc: 24523@debbugs.gnu.org
> 
> 1. emacs -Q
> 2. Visit https://www.base64-image.de/ and "click here" select an image
> (I selected a ~200kB one)
> 3. Click "show code" and copy paste the string you get into *scratch*.
> 4. Now try C-v and M-v as well as type some characters, this is the
> point where it lags.

This creates a single physical line whose length is 280K characters.
It is a known limitation of the Emacs display engine that it's very
slow with such long lines.  See bug #13675.