[ic] Setting email sender address

[Bob Puff]

I have a few different websites running IC on the same server.  When someone
enters an email address at checkout that is invalid, as the hostmaster, I see
the bounce.  I would like to have IC set the email envelope sender for each
catalog, so that bounces go to the appropriate admin for their respective
catalogs (instead of just going to root, or the interch user).