:func:`.validates` function; when set to False, a validation event
will not be triggered if the event was initated as a backref to
an attribute operation from the other side. [ticket:1535]
- break out validation tests into an updated module test_validators

to descriptors, like hybrids, synonyms, composites, user-defined
descriptors, etc.  The attribute
adaptation which goes on has been made more robust, such that if a descriptor
returns another instrumented attribute, rather than a compound SQL
expression element, the operation will still proceed.
Addtionally, the "adapted" operator will retain its class; previously,
a change in class from ``InstrumentedAttribute`` to ``QueryableAttribute``
(a superclass) would interact with Python's operator system such that
an expression like ``aliased(MyClass.x) > MyClass.x`` would reverse itself
to read ``myclass.x < myclass_1.x``.   The adapted attribute will also
refer to the new :class:`.AliasedClass` as its parent which was not
always the case before. [ticket:2872]

by the ORM to iterate mapper hierarchies; under the Jython interpreter
this implementation wasn't ordered, even though cPython and Pypy
maintained ordering.  Also in 0.8.3.
[ticket:2794]

- rework the event system so that event modules load after their
targets, dependencies are reversed
- create an improved strategy lookup system for the ORM
- rework the ORM to have very few import cycles
- move out "importlater" to just util.dependency
- other tricks to cross-populate modules in as clear a way as possible

passes in AliasedInsp and allows more flexibility.
- rework the AliasedClass/AliasedInsp relationship so that AliasedInsp has
all state and functionality.  AliasedClass is just a facade.
[ticket:2756]

the :func:`.aliased` function.  Previously, composite attributes
wouldn't work correctly in comparison operations when aliasing
was applied.  Also in 0.8.2. [ticket:2755]