bug#23594: 25.0.94; Display errors on Linux tty

[Eli Zaretskii]

> Date: Sun, 22 May 2016 16:16:51 +0000
> Cc: 23594@debbugs.gnu.org
> From: Alan Mackenzie <acm@muc.de>
> 
> could it be that the display engine is actually outputting a raw
> 0x0a byte

Of course!  Isn't that what I said at the beginning of this
discussion?

> rather than handling it sensibly?

It was forbidden from doing "sensible" things by the composition
trick.

I think the best fix that is safe for Emacs 25.1 is simply to avoid
displaying the "decomposition" part for low control characters -- they
cannot be composed anyway, AFAIU.