[Open-scap] [patch] Add dpkginfo probe

[Pierre Chifflier]

Hi,

This patch adds the dpkginfo probe to query information from the Debian packages
database.

This probe is mostly inspired from the rpminfo probe.
The apt-pkg library is available only in C++, so the configure script
now checks for the C++ compiler.
The code has been split in two parts to isolate the C++ code, also because one header
(openscap/oscap.h) is using a reserved keyword (namespace) in C++.

It has been basically tested using oscap_cli, but would certainly deserve more
tests.

Patch can be applied using git am

Best regards,
Pierre