vi: Display a vertical line at an arbitrary column width

I'm pretty sure this doesn't work in vi. Vim >= 7.3 only.

By the way, here's the generic version of config (doesn't not error if option is not present):

if exists('&colorcolumn')
    set colorcolumn=80
endif

Extending on @dmedvinsky

if exists('+colorcolumn')
    set colorcolumn=80
else
    au BufWinEnter * let w:m2=matchadd('ErrorMsg', '\%80v.\+', -1)
endif

will emulate colorcolumn by simply coloring the overflowing characters.