Add CVE-2018-1956{5,6,7,8}/dcraw issues

I intentionally added for now only the src:dcraw package itself. Many
other sources embedd src:dcraw (for instace src:rawtherapee) but we need
to check the impact for those.

Details on the reproducers:
https://www.openwall.com/lists/oss-security/2018/11/23/1