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
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/e31193d495f668b2e2e98db290f36af83b6c70e8

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(-)