Updated py-psycopg2 to 2.6.2.

What's new in psycopg 2.6.2
^^^^^^^^^^^^^^^^^^^^^^^^^^^

- Fixed inconsistent state in externally closed connections
  (:tickets:`#263, #311, #443`).
- Report the server response status on errors (such as :ticket:`#281`).
- Raise `!NotSupportedError` on unhandled server response status
  (:ticket:`#352`).
- Allow overriding string adapter encoding with no connection (:ticket:`#331`).
- The `~psycopg2.extras.wait_select` callback allows interrupting a
  long-running query in an interactive shell using :kbd:`Ctrl-C`
  (:ticket:`#333`).
- Fixed `!PersistentConnectionPool` on Python 3 (:ticket:`#348`).
- Fixed segfault on `repr()` of an unitialized connection (:ticket:`#361`).
- Allow adapting bytes using `~psycopg2.extensions.QuotedString` on Python 3
  (:ticket:`#365`).
- Added support for setuptools/wheel (:ticket:`#370`).
- Fix build on Windows with Python 3.5, VS 2015 (:ticket:`#380`).
- Fixed `!errorcodes.lookup` initialization thread-safety (:ticket:`#382`).
- Fixed `!read()` exception propagation in copy_from (:ticket:`#412`).
- Fixed possible NULL TZ decref  (:ticket:`#424`).
- `~psycopg2.errorcodes` map updated to PostgreSQL 9.5.

(wiz)