Split optional dependency descriptions from dependency names before
storing them in the database and use a separate column to store the
descriptions.
This allows us to simplify and optimize the SQL queries in
pkg_dependencies() as well as pkg_required().
Suggested-by: Florian Pritz <bluewind@xinu.at>
Signed-off-by: Lukas Fleischer <lfleischer@archlinux.org>
