Added support to SMF2,

Succesfully exported a SMF2 forum with the following stats :

Export Started: 2013-11-13 12:02:33
Exported Table: User (18919 rows, 00:02.32)
Exported Table: Role (11 rows, 00:00.00)
Exported Table: UserRole (18919 rows, 00:00.56)
Exported Table: Category (35 rows, 00:00.00)
Exported Table: Discussion (14083 rows, 00:02.00)
Exported Table: Comment (52953 rows, 00:03.89)
Exported Table: Media (4688 rows, 00:00.22)
Exported Table: Conversation (4814 rows, 00:00.16)
Exported Table: ConversationMessage (17416 rows, 00:01.19)
Exported Table: UserConversation (34732 rows, 00:00.55)
export_old_smf_2013-11-13_120233.txt.gz
Export Completed: 2013-11-13 12:02:57
Elapsed Time: 00:24.59

One thing to notice, is that user roles are exported, but has no permissions set on Vanilla, so after importation you need to manually set the permissions back again, not sure if this happens with all importations