- removed query.min()/max()/sum()/avg(). these should be called using column argumen...

- removed query.min()/max()/sum()/avg().  these should be called using column arguments or values in conjunction with func.
- fixed [ticket:1008], count() works with single table inheritance
- changed the relationship of InstrumentedAttribute to class such that each subclass in an inheritance hierarchy gets a unique InstrumentedAttribute per column-oriented attribute, including for the same underlying ColumnProperty.  This allows expressions from subclasses to be annotated accurately so that Query can get a hold of the exact entities to be queried when using column-based expressions.  This repairs various polymorphic scenarios with both single and joined table inheritance.
- still to be determined is what does something like query(Person.name, Engineer.engineer_info) do; currently it's problematic.  Even trickier is query(Person.name, Engineer.engineer_info, Manager.manager_name)