[PATCH] Allow transaction to partition table using FDW

Hi,

I would like to use transactions with partitioning table using FDW, but transactions can not be used with the following error.
 'ERROR:  could not serialize access due to concurrent update

So, I tried to write a very simple patch.
This patch works for my purpose, but I do not know if it matches general usage.
I'd like to improve this feature which can be used generally, so please check it.

Please find attached file.

Regards,

-- 
mitani