[COMMITTERS] pgsql: Don't invoke arbitrary code inside a possibly-abortedtransactio

Don't invoke arbitrary code inside a possibly-aborted transaction.

The code here previously tried to call the partitioning operator, but
really the right thing to do (and the safe thing to do) is use
datumIsEqual().

Amit Langote, but I expanded the comment and fixed a compiler warning.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/289992c462b504ffa289202ce8fc34a56b4048c3

Modified Files
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src/backend/catalog/partition.c | 20 ++++++++++++++------
src/backend/utils/adt/datum.c   |  4 ++++
2 files changed, 18 insertions(+), 6 deletions(-)