Review request: Small patch for options_for_select

Can anybody take a quick look at this patch?

http://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/1986

It's a small patch to enable options_for_select to handle grouped options. In short, if an
element of the array passed to options_for_select looks like

["label", [ ... other stuff ...]]

Then it will turn into an optgroup tag, with the given label. The "other stuff" will be the contents
of the optgroup.

This is a little different than grouped_options_for_select, as this allows mixing optgroups and
bare option tags.

Thanks,

--Matt Jones