bug#21471: 25.0.50; bug report with text from Info has spurious escape chars

[Drew Adams <drew.adams@oracle.com>]

> This bug is not a regression, as I get similar behavior with Emacs 24.5 on
> Ubuntu 15.04 (email client Thunderbird 38.2.0) as follows:
...
> The mail that's sent includes strings like this:
> 
> Copyright =C2=A9 1990=E2=80=931996, 1998=E2=80=932014 Free Software Foun=
> dation, Inc.
> 
> even though it's marked "Content-type: text/plain; charset=utf-8;
> format=flowed".  This problem occurs with all non-ASCII characters, not
> merely with curved quotes.

OK, so it's not a regression, in that Unicode chars have
apparently long been copied and pasted incorrectly in this
context.

But Unicode chars were not used all over the place previously,
which makes it a regression of sorts, in observed behavior.
This will bite lots more users a lot more, even if the problem
was potentially present previously as well.

It's a bad bug, interfering considerably with usability,
regardless of whether we want to call it a regression.