pgsql: Restore RI trigger sanity check

Restore RI trigger sanity check

I unnecessarily removed this check in 3de241dba86f because I
misunderstood what the final representation of constraints across a
partitioning hierarchy was to be.  Put it back (in both branches).

Discussion: https://postgr.es/m/201901222145.t6wws6t6vrcu@alvherre.pgsql

Branch
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REL_11_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/04f9b449aa309410dbbcbf4951802a3f73b42bd0

Modified Files
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src/backend/utils/adt/ri_triggers.c | 7 +++++++
1 file changed, 7 insertions(+)