Fixe issues in algebra.tex pointed out by Keenan Kidwell

Thanks to Keenan Kidwell
http://stacks.math.columbia.edu/tag/00P1#comment-715
http://stacks.math.columbia.edu/tag/00SC#comment-716
http://stacks.math.columbia.edu/tag/00ST#comment-717
http://stacks.math.columbia.edu/tag/00T3#comment-718
http://stacks.math.columbia.edu/tag/00T4#comment-720
http://stacks.math.columbia.edu/tag/00T5#comment-721
http://stacks.math.columbia.edu/tag/00TA#comment-724
http://stacks.math.columbia.edu/tag/00TS#comment-725
http://stacks.math.columbia.edu/tag/00TT#comment-726