/usr/local/pgsql/lib/plpgsql.so is the file that allows PLPGSQL stored procedures. This gets loaded by www/doc/sql/postgres.sql to enable these stored procedures. If you look into that file, you'll see that you should fix the path to that plpgsql.so depending on your Postgres installation (/usr/lib/pgsql/plpgsql.so just needs to be uncommented).
Now, the reason why you're getting these errors is because all of your stored procedures loaded incorrectly since you didn't create the PLPGSQL language at the start.
Once you've fixed your postgres.sql file, your best bet is to drop the whole data model and rebuild it. You should then be fine :)
And that's all I have to say about that.