Miscellaneous fixes

I've pushed out an updated version of the Ruby on Rails Tutorial book with lots of miscellaneous fixes, mostly due to reader feedback (which continues to be incredibly helpful). Be sure to reload the pages (and optionally download the PDF after clearing your browser cache) to get the freshest version.

By the way, I usually deploy a new version of the tutorial several times a week, and sometimes several times a day, so the above procedure is probably a good habit to get into. (A little late to tell you, I know. :-) I've added a note to the sidebar of each page (e.g., here) to make it easier to tell when the tutorial was last updated.