Libdpkg has some breaking changes in newer versions which prevented
compiling the deb_packages table on Ubuntu 15.04. This change looks for
the libpkg version user pkg-config and adds some preprocessor magic to
support the newer versions.
This fixes a crash identified by @endrazine.
When apt sources data in /etc/apt/sources.list or /etc/apt/sources.list.d/{*}.list contain invalid data/lines the cache_file.GetPkgCache(); call will fail and cache will be nullptr. Subsequent usage results in a SIGSEV.
To reproduce the fault try:
$ zzuf -I /etc/ -r 0.01:0.1 -s 0:1000 -v \
./build/trusty/osquery/osqueryi --registry_exceptions=true --verbose \
"select count(*) from apt_sources"
Signed-off-by: Jonathan Brossard
