Обсуждение: pgsql: Revert the logic for expanding AND/OR conditions in pred_test()

Log Message:
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Revert the logic for expanding AND/OR conditions in pred_test() to what
it was in 7.4, and add some comments explaining why it has to be this way.
I broke it for OR'd index predicates in a fit of code cleanup last summer.
Per example from Sergey Koshcheyev.

Modified Files:
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    pgsql/src/backend/optimizer/path:
        indxpath.c (r1.167 -> r1.168)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/path/indxpath.c.diff?r1=1.167&r2=1.168)