PostgreSQL v9.0.3 Database Import Error: language "plpgsql" already exists

Hi,

We're planning to upgrade our PostgreSQL database from v8.2.3 to v9.0.3.
Before upgrading our Production server, we're trying out this complete
upgrade process in a separate database server that is just exactly the
replica of the production server.

I already took a dump of our database using pg_dump command in v8.2.3:
"/usr/local/pgsql/bin/pg_dump -D -f dbdump.sql -S mydbuser mydb"

Now, after upgrading PostgreSQL to v9.0.3, I'm trying to import the database
dump using: "psql -f dbdump.sql -o dbdump.log -d mydb -U mydbuser". I'm
getting the following errors while importing:

psql:dbdump.sql:38: ERROR: language "plpgsql" already exists
psql:dbdump.sql:102646: ERROR: attempt to redefine parameter
"plpgsql.variable_conflict"
psql:dbdump.sql:102649: ERROR: function public.plpgsql_call_handler() does
not exist

I also read from 9.0 release notes that PL/pgSQL is now installed by
default.
http://www.postgresql.org/docs/current/interactive/release-9-0.html

My question is, how do I prevent/fix this error during import. Are all
these 3 errors one and the same or are they different errors that each has
to be fixed separately?

NOTE: We've multiple onsite customer servers that has to be upgraded to
v9.0.3, hence I need to address this issue in general.

Regards,
Gnanam