Added a new method :meth:`.Query.select_entity_from` which

Added a new method :meth:`.Query.select_entity_from` which
will in 0.9 replace part of the functionality of
:meth:`.Query.select_from`.  In 0.8, the two methods perform
the same function, so that code can be migrated to use the
:meth:`.Query.select_entity_from` method as appropriate.
See the 0.9 migration guide for details.
[ticket:2736]