Drupal Views Exposed Filter (operators) and CiviCRM Multiple Tags
Indeed, civicrm_handler_filter_pseudo_constant.inc should be altered and

class civicrm_handler_filter_pseudo_constant extends views_handler_filter_in_operator  

should be replaced by 

class civicrm_handler_filter_pseudo_constant extends views_handler_filter_many_to_one 


Funny, I made a pull request in May 2016 (against wrong branch though so it was closed) and made it again in October. Hope this time it will pass.