pgsql: Fix instability in parallel regression tests.

Fix instability in parallel regression tests.

Commit f0c7b789a added a test case in case.sql that creates and then drops
both an '=' operator and the type it's for.  Given the right timing, that
can cause a "cache lookup failed for type" failure in concurrent sessions,
which see the '=' operator as a potential match for '=' in a query, but
then the type is gone by the time they inquire into its properties.
It might be nice to make that behavior more robust someday, but as a
back-patchable solution, adjust the new test case so that the operator
is never visible to other sessions.  Like the previous commit, back-patch
to all supported branches.

Discussion: <5983.1471371667@sss.pgh.pa.us>

Branch
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/68bd9f795d49603941527d1bf357f5e74d164ece

Modified Files
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src/test/regress/expected/case.out |  9 ++++-----
src/test/regress/sql/case.sql      | 11 ++++++-----
2 files changed, 10 insertions(+), 10 deletions(-)