It seems that dev-db/postgresql and dev-db/libpq are now fully masked with the idea towards moving to the dev-db/postgresql-base and dev-db/postgresql-server packages. With that in mind, the howto needs to be rewritten to include these changes. Reproducible: Always
The document has been completely rewritten and has just been pushed to CVS, so it should show up on the site in an hour or so. Thanks to Aaron W. Swenson and Mikkel A. Clausen for the updates.