Complete filetransfer support. Following transfers were tested successfully:
kopete -> kopete
kopete -> gaim
gaim -> kopete
kopete -> Yahoo Messenger 7.5
Yahoo -> Messenger 7.5

There is however still a little issue with receiving files from the Yahoo Messenger:
Sometimes (i think only with pictures) the filename and size is not transmitted in plaintext but somehow encrypted.
The transfer still works but the user has to guess a filename.