While plaing dunnet, saving games via the "save"-command fails with the
message "Error saving to file".  To reproduce:

$  ~/src/emacs/src/emacs -batch -l dunnet

Dead end
You are at a dead end of a dirt road.  The road goes to the east.
In the distance you can see that it will eventually fork off.  The
trees here are very tall royal palms, and they are spaced equidistant
from each other.
There is a shovel here.
>save /tmp/foo.txt
Error saving to file.
>

The reason is that dunnet uses its own implementation of ROT13 to
obfuscate the savefile, and this implementation breaks when it
encounters characters outside the 0-255 range.  On 2015-08-24, Paul
Eggert introduced some curly quotes in data normally saved to this
file.

Attached is a patch that makes dun-rot13 use rot13-region instead of its
own implementation.