pgsql: In HEAD only, revert kluge solution for preventing misuse of

Log Message:
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In HEAD only, revert kluge solution for preventing misuse of pg_get_expr().

A data-type-based solution, which is much cleaner and more bulletproof,
will follow shortly. It seemed best to make this a separate commit though.

Modified Files:
--------------
pgsql/src/backend/parser:
parse_func.c (r1.226 -> r1.227)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parse_func.c?r1=1.226&r2=1.227)
parse_oper.c (r1.114 -> r1.115)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/parse_oper.c?r1=1.114&r2=1.115)
pgsql/src/backend/tcop:
fastpath.c (r1.105 -> r1.106)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/fastpath.c?r1=1.105&r2=1.106)
pgsql/src/include/parser:
parse_func.h (r1.69 -> r1.70)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/parser/parse_func.h?r1=1.69&r2=1.70)