Fix bugs in information_schema.referential_constraints view.

This view was being insufficiently careful about matching the FK constraint
to the depended-on primary or unique key constraint.  That could result in
failure to show an FK constraint at all, or showing it multiple times, or
claiming that it depended on a different constraint than the one it really
does.  Fix by joining via pg_depend to ensure that we find only the correct
dependency.

Back-patch, but don't bump catversion because we can't force initdb in back
branches.  The next minor-version release notes should explain that if you
need to fix this in an existing installation, you can drop the
information_schema schema then re-create it by sourcing
$SHAREDIR/information_schema.sql in each database (as a superuser of
course).

src/backend/catalog/information_schema.sql

@@ -1176,20 +1176,24 @@ CREATE VIEW referential_constraints AS
 
     FROM (pg_namespace ncon
           INNER JOIN pg_constraint con ON ncon.oid = con.connamespace
-          INNER JOIN pg_class c ON con.conrelid = c.oid)
-         LEFT JOIN
-         (pg_constraint pkc
-          INNER JOIN pg_namespace npkc ON pkc.connamespace = npkc.oid)
-         ON con.confrelid = pkc.conrelid
-            AND _pg_keysequal(con.confkey, pkc.conkey)
-
-    WHERE c.relkind = 'r'
-          AND con.contype = 'f'
-          AND (pkc.contype IN ('p', 'u') OR pkc.contype IS NULL)
-          AND (pg_has_role(c.relowner, 'USAGE')
-               -- SELECT privilege omitted, per SQL standard
-               OR has_table_privilege(c.oid, 'INSERT, UPDATE, DELETE, TRUNCATE, REFERENCES, TRIGGER')
-               OR has_any_column_privilege(c.oid, 'INSERT, UPDATE, REFERENCES') );
+          INNER JOIN pg_class c ON con.conrelid = c.oid AND con.contype = 'f')
+         LEFT JOIN pg_depend d1  -- find constraint's dependency on an index
+          ON d1.objid = con.oid AND d1.classid = 'pg_constraint'::regclass
+             AND d1.refclassid = 'pg_class'::regclass AND d1.refobjsubid = 0
+         LEFT JOIN pg_depend d2  -- find pkey/unique constraint for that index
+          ON d2.refclassid = 'pg_constraint'::regclass
+             AND d2.classid = 'pg_class'::regclass
+             AND d2.objid = d1.refobjid AND d2.objsubid = 0
+             AND d2.deptype = 'i'
+         LEFT JOIN pg_constraint pkc ON pkc.oid = d2.refobjid
+            AND pkc.contype IN ('p', 'u')
+            AND pkc.conrelid = con.confrelid
+         LEFT JOIN pg_namespace npkc ON pkc.connamespace = npkc.oid
+
+    WHERE pg_has_role(c.relowner, 'USAGE')
+          -- SELECT privilege omitted, per SQL standard
+          OR has_table_privilege(c.oid, 'INSERT, UPDATE, DELETE, TRUNCATE, REFERENCES, TRIGGER')
+          OR has_any_column_privilege(c.oid, 'INSERT, UPDATE, REFERENCES') ;
 
 GRANT SELECT ON referential_constraints TO PUBLIC;