[Exim] RAV for Exim 4

Don't use RAV antivirus with Exim 4. It drops some recipient addresses,
rewrites sender addresses and even changes (!) some recipient addresses.

I was in contact with GeCAD support and they said that for Exim 4 a new
version of RAV will be released:

RAV Antivirus for Exim is tested on Exim 3.33. For Exim 4 will be
released another version. Please use Exim 3.33 in order to get
RAV working.

--
Kirill