我在 Utopic Unicorn 上，我需要安装 Postgresql 9.3 服务器和客户端。当我尝试自动完成时sudo apt-get install postgres，我只看到 9.4 个包：
postgresql postgresql-autodoc
postgresql-9.4 postgresql-client
postgresql-9.4-asn1oid postgresql-client-9.4
postgresql-9.4-dbg postgresql-client-common
postgresql-9.4-debversion postgresql-common
postgresql-9.4-ip4r postgresql-comparator
postgresql-9.4-orafce postgresql-contrib
postgresql-9.4-pgespresso postgresql-contrib-9.4
postgresql-9.4-pgextwlist postgresql-doc
postgresql-9.4-pgfincore postgresql-doc-9.4
postgresql-9.4-pgmemcache postgresql-filedump
postgresql-9.4-pgmp postgresql-hll
postgresql-9.4-pgpool2 postgresql-plperl-9.4
postgresql-9.4-pgq3 postgresql-plpython3-9.4
postgresql-9.4-pgrouting postgresql-plpython-9.4
postgresql-9.4-pgrouting-doc postgresql-pltcl-9.4
postgresql-9.4-pllua postgresql-prioritize
postgresql-9.4-plproxy postgresql-server-dev-9.4
postgresql-9.4-plr postgresql-server-dev-all
postgresql-9.4-plsh postgres-xc
postgresql-9.4-plv8 postgres-xc-client
postgresql-9.4-postgis-2.1 postgres-xc-contrib
postgresql-9.4-postgis-2.1-scripts postgres-xc-dbg
postgresql-9.4-postgis-scripts postgres-xc-doc
postgresql-9.4-prefix postgres-xc-plperl
postgresql-9.4-preprepare postgres-xc-plpython
postgresql-9.4-repmgr postgres-xc-pltcl
postgresql-9.4-slony1-2 postgres-xc-server-dev
我如何安装他们的 9.3 版本？