Postmodern changes affecting clsql-postgresql-socket3

cl-postgres now exports another symbol, POSTGRESQL-NOTIFICATION, related
to the Postgres listen/notify mechanism. This causes a problem with
clsql-postgres-socket, which uses POSTGRESQL-NOTIFICATION to name its
own condition which has an incompatible superclass structure.

It looks to me like cl-postgresql-socket3's package already shadows
POSTGRESQL-WARNING. I think shadowing POSTGRESQL-NOTIFICATION would
suffice to fix this new issue.

What do you think?

Thanks,
Zach