[psycopg] Psycopg 2.7.1 released

A quick bugfix release to solve some teething problem with some of the
changes introduced in 2.7:

- Ignore None arguments passed to connect() and make_dsn() (ticket #517).
- OpenSSL upgraded from major version 0.9.8 to 1.0.2 in the Linux
wheel packages (ticket #518).
- Fixed build with libpq versions < 9.3 (ticket #520).

Code fresh to grab at:

- source package:
http://initd.org/psycopg/tarballs/PSYCOPG-2-7/psycopg2-2.7.1.tar.gz
- signature: http://initd.org/psycopg/tarballs/PSYCOPG-2-7/psycopg2-2.7.1.tar.gz.asc

Enjoy the release!

-- Daniele