[exim] ClamAV and Exim4.34

Hi folks,

I have exim4.34 running at a client. I know I should upgrade the machine
to 4.5x, but they have had such problems that I am really wanting to get
their service settled into a smooth operating pattern before attempting
the next upheaval.

My problem is that the information I could find with regard to ClamAV
and Exim4 relates primarily to 4.5x and not 4.34. The av_scanner
directive is not available (or at least me config file complains) when I
use it.

How does one go about installing ClamAV in 4.34?
Pointers will be welcome.

Thanks
Hamish