update_virus_scanners not finding clamavmodule

[Gareth]

The update_virus_scanners broke after an upgrade last month. Virus
scanning is still working but the update script is not finding
clamavmodule.

The virus scanners conf file contains :-

clamav          /usr/lib/MailScanner/clamav-wrapper     /usr/local/bin
clamd           /bin/false                              /usr/local/bin
clamavmodule    /bin/false                              /tmp

clamav is installed in /usr/local/bin