- Identified an inconsistency when handling :meth:`.Query.join` to the

- Identified an inconsistency when handling :meth:`.Query.join` to the
same target more than once; it implicitly dedupes only in the case of
a relationship join, and due to :ticket:`3233`, in 1.0 a join
to the same table twice behaves differently than 0.9 in that it no
longer erroneously aliases.   To help document this change,
the verbiage regarding :ticket:`3233` in the migration notes has
been generalized, and a warning has been added when :meth:`.Query.join`
is called against the same target relationship more than once.
fixes #3367