visual mark for column > 80

[Micha Feigin]

I want to mark the transition to lines over 80 characters with either a
vertical line or a change of background color.

The idea is to keep code below 80 characters where fill mode doesn't do the
job. I want a visual of which lines are too long but it a way that won't ruin
syntax coloring in the rare cases where I'm willing to accept this manually.

thanks