Relax restriction (8) on the push-down optimization so that it only applies

Relax restriction (8) on the push-down optimization so that it only applies
if one or more columns uses a collating sequence other than BINARY.
See [forum:/forumpost/3824ced748baa808|forum post 3824ced748baa808] and
check-in [346a3b12b861ce7b].

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