pgsql: Fix yet another corner case in dumping rules/views with USING cl

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).

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/91e16b980612d80de1017e97e9f206239afb9026

Modified Files
--------------
src/backend/utils/adt/ruleutils.c | 49 ++++++++++++++++++++++-------
src/test/regress/expected/create_view.out | 34 ++++++++++++++++++++
src/test/regress/sql/create_view.sql | 18 +++++++++++
3 files changed, 90 insertions(+), 11 deletions(-)