pgsql: Don't try to constant-fold functions returning RECORD, since the

Log Message:
-----------
Don't try to constant-fold functions returning RECORD, since the optimizer
isn't presently set up to pass them an expected tuple descriptor. Bug has
been there since 7.3 but was just recently reported by Thomas Hallgren.

Tags:
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REL7_3_STABLE

Modified Files:
--------------
pgsql/src/backend/optimizer/util:
clauses.c (r1.109 -> r1.109.2.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/clauses.c.diff?r1=1.109&r2=1.109.2.1)