Readme update, several bugfixes and a security issue fixed.

  * Readme: added a note to enable the domain in the recaptcha account
            in order to use the keys. Otherwise they won't work.
  * Bugfixes:  - missing argument in the CachReport class
               - access to undefined array index
               - workaround for misfunctioning require_once call
  * Security:  it was possible to inject shell code into a space cron
               now a alphanumerical value will be used instead of the
               full original space name so $space in a space cron is
               no longer representing an array index