Fix docs for detecting whether pyrex is installed
Fix docs for detecting whether pyrex is installed

sparkslabs/kamaelia,sparkslabs/kamaelia,sparkslabs/kamaelia,sparkslabs/kamaelia,sparkslabs/kamaelia,sparkslabs/kamaelia,sparkslabs/kamaelia,sparkslabs/kamaelia,sparkslabs/kamaelia,sparkslabs/kamaelia