pgsql: Don't cache per-group context across the whole query in ordereds

Don't cache per-group context across the whole query in orderedsetaggs.c.

Although nodeAgg.c currently uses the same per-group memory context for
all groups of a query, that might change in future.  Avoid assuming it.
This costs us an extra AggCheckCallContext() call per group, but that's
pretty cheap and is probably good from a safety standpoint anyway.

Back-patch to 9.4 in case any third-party code copies this logic.

Andrew Gierth

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/ecd657974478fc713fdc3a625d648cd6a985e3e6

Modified Files
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src/backend/utils/adt/orderedsetaggs.c |   28 +++++++++++++++-------------
1 file changed, 15 insertions(+), 13 deletions(-)