Add support for Ubuntu 14.04

.. by having nipapd depend on postgresql-9.1-ip4r OR postgresql-9.3-ip4r
instead of just on the 9.1 package. Should perhaps also work on Debian
unstable (which seem to feature both postgresql-9.3 or 9.4).

Fixes #568.
Merge pull request #569 from plajjan/568-fix-postgres-depends

Add support for Ubuntu 14.04