Theme the group links in apachesolr search results

This patch solves a bug where search results will always say '0 groups' and adds a feature by allowing for a better group list display in the search results, by using hook_apachesolr_process_results() and calling theme_apachesolr_nodeaccess_og_list().

A small fix to og module, needed by this patch, has been committed: http://drupal.org/node/334090