Adding a hook_status hook, and page to view system status information.

  Modified invoke_hook() function to return possible results of invoking the hook.

  Finished update_status module, so that it effectively talks to getflightpath.com,
  to discover which modules need updates.

2013-03-09
  Fixed unclosed <a> tag in install.php.

  Modified the places where call_user_func was being called with a referenced variable;
  changed it to a more PHP 5.4 friendly technique, so FP will be compatible with PHP 5.4.

  Updated hooks.api.php file to contain all of the hooks in FP, with explanations.