Obsolete comment in postgres_fdw.c

Hi,

Here is the comments for foreign_join_ok in postgres_fdw.c:

/*
 * Assess whether the join between inner and outer relations can be
pushed down
 * to the foreign server. As a side effect, save information we obtain
in this
 * function to PgFdwRelationInfo passed in.
 *
 * Joins that satisfy conditions below are safe to push down.
 *
 * 1) Join type is INNER or OUTER (one of LEFT/RIGHT/FULL)
 * 2) Both outer and inner portions are safe to push-down
 * 3) All foreign tables in the join belong to the same foreign server
and use
 *    the same user mapping.
 * 4) All join conditions are safe to push down
 * 5) No relation has local filter (this can be relaxed for INNER JOIN,
if we
 *    can move unpushable clauses upwards in the join tree).
 */

The condition 3 is now checked by the core, so I'd like to remove that
condition from the above comments.

In addition, I'd like to update some related comments in
src/include/nodes/relation.h and src/backend/optimizer/path/joinpath.c.

Attached is a patch for that.

Best regards,
Etsuro Fujita