pgsql: Fix mishandling of after-trigger state when a SQL function

Log Message:
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Fix mishandling of after-trigger state when a SQL function returns multiple
rows --- if the surrounding query queued any trigger events between the rows,
the events would be fired at the wrong time, leading to bizarre behavior.
Per report from Merlin Moncure.

This is a simple patch that should solve the problem fully in the back
branches, but in HEAD we also need to consider the possibility of queries
with RETURNING clauses.  Will look into a fix for that separately.

Tags:
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REL8_0_STABLE

Modified Files:
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    pgsql/src/backend/executor:
        functions.c (r1.91.4.1 -> r1.91.4.2)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/functions.c.diff?r1=1.91.4.1&r2=1.91.4.2)