Declare variables compatible with Domain Access

Opening new issue, as requested on http://drupal.org/node/1702522#comment-6746576

A recurrent question has been the integration for Google Analytics module with Domain Access.
The work has been done for the 6.x version through Domain Config, however the way to go on Drupal 7 is using Variable and Domain Variable module.
Google Analytics has already been integrated with Variable for i18N purposes: http://drupal.org/node/595520 - http://drupal.org/node/1702522
An additional parameter is needed to show up with Domain realm declared on Domain Variable ('multidomain' => TRUE, ) #1809794: Making Custom variables available in Config form

I have modified the googleanalytics.variable.inc file on line 20 adding a new parameter 'multidomain' => TRUE,' and it works for me.
I'm not skilled enough (yet) to produce a standard drupal patch, hope that will help others, though.