Typos and clarification

Thanks to Keenan Kidwell
http://stacks.math.columbia.edu/tag/06RU#comment-734
http://stacks.math.columbia.edu/tag/01WS#comment-735
http://stacks.math.columbia.edu/tag/056N#comment-736
http://stacks.math.columbia.edu/tag/04KM#comment-738
http://stacks.math.columbia.edu/tag/030W#comment-740