Added DOS vulnerability
Added DOS vulnerability

Added a sleep to the show messages page to show how using slow blocking
methods can allow DOS to occur.

OWASP/railsgoat,jasnow/railsgoat,cktricky/railsgoat,jasnow/railsgoat,OWASP/railsgoat,jasnow/railsgoat,OWASP/railsgoat,OWASP/railsgoat,cktricky/railsgoat,cktricky/railsgoat,jasnow/railsgoat,cktricky/railsgoat