Add to and from dates to the Relationship Report filter

The Relationship Report as currently configured does not allow for expired or not yet started relationships. This change adds a Relationship Valid (i.e. has it started and has it not ended?) and Start and End Dates to the filter.

I attach a patch file (against 4.6.9) that will, I hope, apply the changes to "<joomla root>/administrator\components/com_civicrm/civicrm/CRM/Report/Form/Contact/Relationship.php" or the equivalent in Drupal and Wordpress. I also attach a screenshot of what the filter screen looks like.