DragonFlyBSD

Some UTF-8 characters cannot be displayed in xterms

My setup:

DragonFly 4.3-DEVELOPMENT v4.3.1.278
LANG=en_US.UTF-8

Detailled problem description:

mail/mutt running in an xterm cannot display vertical and horizontal lines used to represent email conversation threads

At least these four characters are involved:
- ─ (U+2500) as in http://www.fileformat.info/info/unicode/char/2500/index.htm
- │ (U+2502) as in http://www.fileformat.info/info/unicode/char/2502/index.htm
- └ (U+2514) as in http://www.fileformat.info/info/unicode/char/2514/index.htm
- ├ (U+251C) as in http://www.fileformat.info/info/unicode/char/251C/index.htm

Changing the locale to en_US.US-ASCII allows mutt to display these characters or their ascii variants