Fixed #8154: Added note to docs/db-api.txt indicating that reverse() is only...

that mode of access (slicing from the end), because it's not possible to do it

efficiently in SQL.

Also, note that ``reverse()`` should generally only be called on a

``QuerySet`` which has a defined ordering (e.g., when querying against

a model which defines a default ordering, or when using

``order_by()``). If no such ordering is defined for a given

``QuerySet``, calling ``reverse()`` on it has no real effect (the

ordering was undefined prior to calling ``reverse()``, and will remain

undefined afterward).

``distinct()``

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