pgsql: Improve regression test case to avoid depending on system catalo

Improve regression test case to avoid depending on system catalog stats.

In commit 95f4e59c32866716 I added a regression test case that examined
the plan of a query on system catalogs. That isn't a terribly great idea
because the catalogs tend to change from version to version, or even
within a version if someone makes an unrelated regression-test change that
populates the catalogs a bit differently. Usually I try to make planner
test cases rely on test tables that have not changed since Berkeley days,
but I got sloppy in this case because the submitted crasher example queried
the catalogs and I didn't spend enough time on rewriting it. But it was a
problem waiting to happen, as I was rudely reminded when I tried to port
that patch into Salesforce's Postgres variant :-(. So spend a little more
effort and rewrite the query to not use any system catalogs. I verified
that this version still provokes the Assert if 95f4e59c32866716's code fix
is reverted.

I also removed the EXPLAIN output from the test, as it turns out that the
assertion occurs while considering a plan that isn't the one ultimately
selected anyway; so there's no value in risking any cross-platform
variation in that printout.

Back-patch to 9.2, like the previous patch.

Branch
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REL9_4_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/3bfd40180859e252090f072805ec24b16c360f2f

Modified Files
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src/test/regress/expected/join.out | 56 +++++++++---------------------------
src/test/regress/sql/join.sql | 30 ++++++-------------
2 files changed, 22 insertions(+), 64 deletions(-)