pgsql: Properly initialize SortSupport for ORDER BY rechecks in nodeInd

Properly initialize SortSupport for ORDER BY rechecks in nodeIndexscan.c.

Fix still another bug in commit 35fcb1b3d: it failed to fully initialize
the SortSupport states it introduced to allow the executor to re-check
ORDER BY expressions containing distance operators. That led to a null
pointer dereference if the sortsupport code tried to use ssup_cxt. The
problem only manifests in narrow cases, explaining the lack of previous
field reports. It requires a GiST-indexable distance operator that lacks
SortSupport and is on a pass-by-ref data type, which among core+contrib
seems to be only btree_gist's interval opclass; and it requires the scan
to be done as an IndexScan not an IndexOnlyScan, which explains how
btree_gist's regression test didn't catch it. Per bug #14134 from
Jihyun Yu.

Peter Geoghegan

Report: <20160511154904(dot)2603(dot)43889(at)wrigleys(dot)postgresql(dot)org>

Branch
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REL9_5_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/a7aa61ffe7ed12cf8d5cbdfc887900549f9ed354

Modified Files
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contrib/btree_gist/expected/interval.out | 18 ++++++++++++++++++
contrib/btree_gist/sql/interval.sql | 6 ++++++
src/backend/executor/nodeIndexscan.c | 15 +++++++++++++--
3 files changed, 37 insertions(+), 2 deletions(-)