use include_once path relative to Drupal root

Relativity currently includes the relativity_views.inc file as:

  include_once('relativity_views.inc');

Unfortunately this causes issues on hosts with security restrictions on paths in the include_path as these directories are scanned first looking for the file. Changing the include_once to use a relative path (to the current working directory, which is gets rid of the issue and saves scanning all the other directories before looking in the current directory:

  include_once('./'. drupal_get_path('module', 'relativity') .'/relativity_views.inc');

The attached patch implements this change for the DRUPAL-5 branch.

Cheers,
Eric