pgsql: Fix planning of btree index scans using ScalarArrayOpExpr quals.

Fix planning of btree index scans using ScalarArrayOpExpr quals.

In commit 9e8da0f75731aaa7605cf4656c21ea09e84d2eb1, I improved btree
to handle ScalarArrayOpExpr quals natively, so that constructs like
"indexedcol IN (list)" could be supported by index-only scans. Using
such a qual results in multiple scans of the index, under-the-hood.
I went to some lengths to ensure that this still produces rows in index
order ... but I failed to recognize that if a higher-order index column
is lacking an equality constraint, rescans can produce out-of-order
data from that column. Tweak the planner to not expect sorted output
in that case. Per trouble report from Robert McGehee.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/807a40c551dd30c8dd5a0b3bd82f5bbb1e7fd285

Modified Files
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src/backend/optimizer/path/indxpath.c | 15 ++++++++-
src/test/regress/expected/create_index.out | 45 ++++++++++++++++++++++++++++
src/test/regress/sql/create_index.sql | 24 +++++++++++++++
3 files changed, 83 insertions(+), 1 deletions(-)