I had second thoughts on the "data family export" question.
Rather than add a wierd special case it seems better to be
simple and consistent.  So this patch

 * Reverts to the simple behaviour:
     module M where { ... }
   exports only what is defined in M, ie NOT any
   imported data families.
   See Note [Exports of data families] in RnNames

* Documents this behaviour in the user manual, and clarifies
  what was there before.