Adding the "api" parameter is also useful if you want to copy the URL to someone else. So you can write such things as: http://sa.column80.com/?q=1860&api=77 Now it is a URL that can be copied to someone else that is not on the same session.
I found out how to do without cookies: Add the "api" parameter to the query string when retrieving a message. You might have to do manually every time, unless you can write a program to do for you.
I have never made these kind of mistakes. I have done the things in section 2 and section 19, but I did it on purpose and expected the result, it was not a mistake.
I use Enhanced CWEB for C programming. Many of these things will be caught because you can see in the printout of the book, that there are mistakes. (For example, it typesets octal numbers in italic)
I say GPL so that you can merge anyone else's improvements (including those by other companies and they make the software publicly available by same license, too), you can sell the software with warranty and/or printed documentation and/or DVD with the software on it, and everyone else can do the same. If you do not need this, you can use a simple license instead (such as MIT license)