pgsql: Don't try to constant-fold functions returning RECORD.

Log Message:
-----------
Don't try to constant-fold functions returning RECORD.  We were never
able to do this before, but I had tried to make an exception for functions
with OUT parameters.  Michael Fuhr found one problem with it already, and
I found another, which was it didn't work for strict functions with a
NULL input.  While both of these could be worked around, the probability
that there are more gotchas seems high; I think prudence dictates just
reverting to the former behavior for now.  Accordingly, remove the kluge
added to get_expr_result_type() for Michael's case.

Modified Files:
--------------
    pgsql/src/backend/optimizer/util:
        clauses.c (r1.199 -> r1.200)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/clauses.c.diff?r1=1.199&r2=1.200)
    pgsql/src/backend/utils/fmgr:
        funcapi.c (r1.23 -> r1.24)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/fmgr/funcapi.c.diff?r1=1.23&r2=1.24)