[vim] :se num -> underlined numbers

[Graham Ashton <graham@mirror.bt.co.uk>]

I've got vim installed on both hamm and slink boxes, versions 5.0 and
5.3 of vim respectively, and use both from the same remote rxvt session.

When I switch line numbering on in 5.0, everything looks fine. When I
switch it on in 5.3, the line numbers themselves are underlined. It's
really annoying.

I've got syntax highlighting turned off. Can anybody suggest why line
numbers are underlined in 5.3, but not in 5.0? I think it must be an
entry in /etc/vimrc, but can't figure out which one.

-- 
Graham