Merged [13559]: Fixed test for hiding of a metacontact from the list when it has...

Merged [13559]: Fixed test for hiding of a metacontact from the list when it has no contained contacts [i.e. after the contacts are deleted or the accounts all sign off] and improved efficiency for the general AIListContact check. A particular use case that would previously lead to a (null) contact in the list was when deleting a metacontact which contained 2 AIListContacts, each with the same UID, on 2 different Yahoo accounts. Deletion now works as expected (after [13556]) and then the metacontact disappears as expected.

git-svn-id: svn://svn.adiumx.com/adium/branches/adium-0.8@13564 1c916fce-81e2-0310-a464-8ca513f45935