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

Log Message:
-----------
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.

Modified Files:
--------------
    pgsql/src/backend/executor:
        functions.c (r1.107 -> r1.108)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/functions.c.diff?r1=1.107&r2=1.108)