Notify user on virus upload

Hello,

if clam av is configured and is scaning files on upload the current method to inform users isn't enough.

I know that the alert is visible in the admin interface but the notification for the actual user is not clear, i think the sync client only reports "upload failed" instead of the proper notification.

In some cases this notification can be important enough to be send as e-mail alongside a proper notification from the client or webinterface.