Make use of Express@2.5 style of relative path for partials.

Recently upgraded from express 2.x to 3.x and found that having this small change in place really eased the transition for me because I didn't have to go add preceding slashes to every partial / include in my site. We could change to use `options.settings.views` instead of `options.settings['views']` if you want to be really particular. Otherwise the only other thing I had to change was `res.render('x',{ layout: 'y' })` is now: `res.render('x',{ _layoutFile: 'y' })` ...easy to replace using sed -i so not a big deal.

Thanks for this repo. It was a huge help in migrating from 2.x to 3.x, hopefully this patch helps someone else down the line who also might have piggy-backed of the `app.use('views', xxxx)` feature of express 2.x like I did to augment relative paths for partials.