Fix up btree's initial scankey processing to be able to detect redundant

Tom Lane <tgl@sss.pgh.pa.us>

Commit: 9aefd56669131bfe8dd234544fb87e848a781c97
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date: 2006-12-28T23:16:39Z
Releases: 8.3.0
Fix up btree's initial scankey processing to be able to detect redundant
or contradictory keys even in cross-data-type scenarios.  This is another
benefit of the opfamily rewrite: we can find the needed comparison
operators now.

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