Install docs should warn against PyPgSQL, or maybe Trac should assert

[Dave Abrahams <dave@…>]

I've seen problems similar to the one described in http://bitten.edgewall.org/ticket/198 many times now in various contexts, and have spent hours and hours trying to debug them, to no avail. Installing psycopg2 made them all disappear. I don't know where the bug is, and of course it would be better to have real answers, but based on my experience I would be prepared to declare Trac incompatible with PyPgSQL,

[cboos]

See #5096. I'll update the docs.