Fixes listcommands; status 500 error

Some people <a href="http://chat.stackoverflow.com/transcript/message/13154994#13154994">with really long names</a> are getting a status 500 error on listcommands, because a 20 char buffer zone is not enough. This <a href="http://chat.stackoverflow.com/transcript/message/13155861#13155861">patch fixes that</a>, by taking username lengths into account.