pgsql: Add isolation tests for DROP INDEX CONCURRENTLY.

Add isolation tests for DROP INDEX CONCURRENTLY.
Backpatch to 9.2 to ensure bugs are fixed.

Abhijit Menon-Sen

Branch
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REL9_2_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/d4412fa0e543fa1608c3bb9b6651d247ce59983f

Modified Files
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.../expected/drop-index-concurrently-1.out         |   36 ++++++++++++++++++++
.../expected/drop-index-concurrently-2.out         |   24 +++++++++++++
src/test/isolation/isolation_schedule              |    2 +
.../isolation/specs/drop-index-concurrently-1.spec |   33 ++++++++++++++++++
.../isolation/specs/drop-index-concurrently-2.spec |   21 +++++++++++
5 files changed, 116 insertions(+), 0 deletions(-)