Trigger a notification for file uploads to Trac

[johnbillion]

We've spent years trying to educate users that uploading a file to Trac doesn't trigger a notification, and you therefore need to update the ticket afterwards (eg. with a comment or a keyword change).

Instead, Trac should be made to send out a notification to the appropriate ticket when a file is uploaded. Is this possible?

[ocean90]

Duplicate of #1606.