Issue with DateStyle and pgbouncer

Hello,

trawling on twitter and lurking on github I've intercepted some cries
of pain caused by psycopg+pgbouncer regarding DateStyle. psycopg only
works with ISO style dates: usually it knows the DateStyle on
connection [1] and changes it if the setting isn't compatible.
Unfortunately pgbouncer doesn't send the DateStyle setting on
connection, and psycopg conservatively sets DateStyle to ISO when the
information is missing: on pgbouncer this may mean an extra query
every query. Not amusing.

Because I'm going to release version 2.5 soon, so it's a good time to
break something. What I'd do is: if the DateStyle info is missing
(i.e. you are on pgbouncer or other "broken" middleware) just assume
the date style is correct. This would break dates adaptation for users
of a database with non-standard DateStyle (e.g. "German") running
through pgbouncer: for these users there is an easy fix: pass the
extra DateStyle=ISO option at connection, either in the connection
string:

    psycopg2.connect("host=here user=that options='-c DateStyle=ISO' ")

or as an extra connection parameter:

    psycopg2.connect(host="here" user="that" options="-c DateStyle=ISO")

or using an env variable:

    $ export PGOPTIONS='-c DateStyle=ISO'
    ...
    >>> psycopg2.connect(DSN) # unchanged

It's a one char change in the code and a quite tricky case to document...

Comments?

Thank you,

-- Daniele

[1] http://www.postgresql.org/docs/current/static/libpq-status.html#LIBPQ-PQPARAMETERSTATUS