[Dillo-dev] patch: optgroup for OptionMenu

I've had this kicking around in my tree for months...finally got around to implementing the max string width for OptionMenu and doing a little polishing. Here it treats optgroup, option, and /optgroup as types of options because when I tried keeping options inside optgroup structures, it turned out to be messier. The idea is that if this is accepted, I will later do some renaming. (Not enabled for ListResource yet because the straightforward approach did not result in something very usable...)