Multi-Org segregation failures: Duplicate checking & import

See http://forum.civicrm.org/index.php/topic,12273.0.html

Actual behaviour:
Dupe matching operates across all sites in a multi-site Civi. So no way to match within a site, which is needed in order to import. Effectively stops any imports from working once we have one site's data in the multi-site civi, if there's any chance of a contact in site A matching a contact in site B.

Desired behaviour:
Dupe matching should respect ACLs in the same way that other operations do. So if the user only has permission to view site A's contacts then a dupe check or import done by that user should only match against site A's contacts.

Dave J