* only package names are matched, versions are not matched
 * Gentoo packages are only mapped to Debian Source packages. This means that
   you get a list of Debian source packages as build dependencies. Those
   source packages have later to be mapped to binary packages.
 * software in Gentoo that's not in Debian
 * software in Debian that's not in Gentoo
 * different source package splittings
 * disjunctive dependencies not handled yet