Fix yet another corner case in dumping rules/views with USING clauses.

ruleutils.c tries to cope with additions/deletions/renamings of columns in
tables referenced by views, by means of adding machine-generated aliases to
the printed form of a view when needed to preserve the original semantics.
A recent blog post by Marko Tiikkaja pointed out a case I'd missed though:
if one input of a join with USING is itself a join, there is nothing to
stop the user from adding a column of the same name as the USING column to
whichever side of the sub-join didn't provide the USING column.  And then
there'll be an error when the view is re-parsed, since now the sub-join
exposes two columns matching the USING specification.  We were catching a
lot of related cases, but not this one, so add some logic to cope with it.

Back-patch to 9.3, which is the first release that makes any serious
attempt to cope with such cases (cf commit 2ffa740be and follow-ons).

src/test/regress/expected/create_view.out

@@ -1298,6 +1298,40 @@ select pg_get_viewdef('vv5', true);
       JOIN tt10 USING (x);
 (1 row)
 
+--
+-- Another corner case is that we might add a column to a table below a
+-- JOIN USING, and thereby make the USING column name ambiguous
+--
+create table tt11 (x int, y int);
+create table tt12 (x int, z int);
+create table tt13 (z int, q int);
+create view vv6 as select x,y,z,q from
+  (tt11 join tt12 using(x)) join tt13 using(z);
+select pg_get_viewdef('vv6', true);
+      pg_get_viewdef       
+---------------------------
+  SELECT tt11.x,          +
+     tt11.y,              +
+     tt12.z,              +
+     tt13.q               +
+    FROM tt11             +
+      JOIN tt12 USING (x) +
+      JOIN tt13 USING (z);
+(1 row)
+
+alter table tt11 add column z int;
+select pg_get_viewdef('vv6', true);
+        pg_get_viewdef        
+------------------------------
+  SELECT tt11.x,             +
+     tt11.y,                 +
+     tt12.z,                 +
+     tt13.q                  +
+    FROM tt11 tt11(x, y, z_1)+
+      JOIN tt12 USING (x)    +
+      JOIN tt13 USING (z);
+(1 row)
+
 -- clean up all the random objects we made above
 set client_min_messages = warning;
 DROP SCHEMA temp_view_test CASCADE;

src/test/regress/sql/create_view.sql

@@ -417,6 +417,24 @@ alter table tt9 drop column xx;
 
 select pg_get_viewdef('vv5', true);
 
+--
+-- Another corner case is that we might add a column to a table below a
+-- JOIN USING, and thereby make the USING column name ambiguous
+--
+
+create table tt11 (x int, y int);
+create table tt12 (x int, z int);
+create table tt13 (z int, q int);
+
+create view vv6 as select x,y,z,q from
+  (tt11 join tt12 using(x)) join tt13 using(z);
+
+select pg_get_viewdef('vv6', true);
+
+alter table tt11 add column z int;
+
+select pg_get_viewdef('vv6', true);
+
 -- clean up all the random objects we made above
 set client_min_messages = warning;
 DROP SCHEMA temp_view_test CASCADE;