Create plpgsql language if not available

This should fix the problem in Travis CI server.
(http://travis-ci.org/#!/rails/rails/jobs/1194988)

activerecord/test/schema/postgresql_specific_schema.rb

@@ -127,6 +127,7 @@ _SQL
   );
 _SQL
 
+begin
     execute <<_SQL
     CREATE TABLE postgresql_partitioned_table_parent (
       id SERIAL PRIMARY KEY,
@@ -148,7 +149,14 @@ _SQL
       BEFORE INSERT ON postgresql_partitioned_table_parent
       FOR EACH ROW EXECUTE PROCEDURE partitioned_insert_trigger();
 _SQL
-
+rescue ActiveRecord::StatementInvalid => e
+  if e.message =~ /language "plpgsql" does not exist/
+    execute "CREATE LANGUAGE 'plpgsql';"
+    retry
+  else
+    raise e
+  end
+end
 
   begin
     execute <<_SQL