clamav - security update

Upstream published version 0.98.7. This update updates sqeeze-lts to the
latest upstream release in line with the approach used for other Debian
releases.

The changes are not strictly required for operation, but users of the previous
version in Squeeze may not be able to make use of all current virus signatures
and might get warnings.

The bug fixes that are part of this release include security fixes related
to packed or crypted files (CVE-2014-9328, CVE-2015-1461, CVE-2015-1462,
CVE-2015-1463, CVE-2015-2170, CVE-2015-2221, CVE-2015-2222, and CVE-2015-2668)
and several fixes to the embedded libmspack library, including a potential
infinite loop in the Quantum decoder (CVE-2014-9556).

If you use clamav, we strongly recommend that you upgrade to this version.