Backspace in wimenu deletes bytes instead of code points

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Switch to an international keyboard, e.g. "setxkbmap fr"
2. echo foo | wimenu
3. Insert "é" using the "2" key
4. Press backspace

What is the expected result? What do you see instead?
After step 2, foo is visible, as expected.
After step 3, foo isn't visible, as expected.
After step 4, foo still isn't visible. You need to press backspace again to 
show it.

I assume this is because "é" takes two bytes, and backspace only deleted the 
first one. This is just a guess, though -- the issue title might be wrong.

What version of the product are you using (wmii -v)? On what operating
system (uname -a)?
wmii-3.9.2, ©2010 Kris Maglione
Linux my_hostname 3.6.10-1-ARCH #1 SMP PREEMPT Tue Dec 11 10:19:36 CET 2012 
i686 GNU/Linux


Please provide any additional information below.

$ locale
LANG=en_US.UTF-8
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_COLLATE=C
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_PAPER="en_US.UTF-8"
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT="en_US.UTF-8"
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=

Cursor keys behave strangely too. It seems they also operate in terms of bytes 
instead of code points.

NB: Unicode also has combining characters that allow a single glyph made of 
multiple code points -- I can't even guess what issues will happen there. But 
"é" is just a single run-of-the-mill BMP code point, so that should be easier 
to fix.

Possibly related to Issue 181.

Original issue reported on code.google.com by [email protected] on 28 Dec 2012 at 6:22