bug#24953: 25.1; Possible inefficiency in UTF-8

[Eli Zaretskii <eliz@gnu.org>]

> From: Eli Barzilay <eli@barzilay.org>
> Date: Tue, 15 Nov 2016 23:25:35 -0500
> 
> In an empty buffer, insert a pile of "foo" lines (a few screens high),
> in the middle, add the result of (insert #x23ce) (to get the unicode
> character).  Now `C-x RET l' and "UTF-8".

Regardless of the issue reported here, I would advise against setting
the UTF-8 language environment on MS-Windows.  Doing so is likely to
screw you in some situations.  For example, that sets up the encoding
of communications with subprocesses to use UTF-8, something that only
works with pure ASCII text and command-line arguments, and breaks
otherwise on Windows.

You shouldn't need to do this, not in Emacs 25 anyway.

> Now, just moving the cursor around in the buffer shows very
> noticeable delays, up to more than a second.  In the default
> language of "English" I don't see that happening.  This is on a
> Windows 7 machine.

Fixed on the emacs-25 branch.  The reason was sub-optimal definition
of the default fontset wrt to fonts that cover symbols and punctuation
Unicode blocks.

Thanks.