Removed whitespace on the ends of lines.

There were many lines (mostly in comments) that ended with spaces.  When
using an editor that highlights whitespace on the ends of lines, there
were many lines that were highlighted.

This commit removes all the extraneous whitespace.

(Hint: in github, you can add &w=1 to the end of url showing a diff to get the diff ignoring changes in whitespace.  If you look at the diff of this commit, you can double-check that I only removed whitespace.)