so remove them from MergeJoin node.  Hack together a partial
solution for commuted mergejoin operators --- yesterday
a mergejoin int4 = int8 would crash if the planner decided to
commute it, today it works.  The planner's representation of
mergejoins really needs a rewrite though.
Also, further testing of mergejoin ops in opr_sanity regress test.

From: Tatsuo Ishii <t-ishii@sra.co.jp>

Ok. I made patches replacing all of "#if FALSE" or "#if 0" to "#ifdef
NOT_USED" for current. I have tested these patches in that the
postgres binaries are identical.

A test case is:
create table linetab (x line);
select * from linetab where ?| x;
which coredumps in 6.4.2 and current sources.

but it saves almost 10% of the runtime in Charles Hornberger's optimizer
example, so what the heck ...