BUG #14249: In FDW, variable not found in subplan target list

The following bug has been logged on the website:

Bug reference: 14249
Logged by: Wayne Warren
Email address: wayne(dot)warren(at)multiscalehn(dot)com
PostgreSQL version: 9.6beta2
Operating system: Ubuntu 14
Description:

I have written a foreign data wrapper that works with version 9.5.2. Now
with 9.6beta2 I receive "ERROR: variable not found in subplan target list"
when I refer to a column in the WHERE clause that is not also listed as a
target column:

mydb=# select record_id, addr_chg_user_id from si_ept_470
where addr_chg_instant='5441342125';
ERROR: variable not found in subplan target list

When the column is included in the target list, the correct results are
produced.