of a declarative inheritance hierarchy would prevent attributes
and configuration being correctly propagated from the base class
to the inheriting class.
fixes #3219 fixes #3240

subclass, the value returned by the descriptor is not available
because the superclass is already mapped with the InstrumentedAttribute,
until the subclass is mapped.  We add a setattr() to set up that
attribute so that the __mapper_args__ hook and possibly others
have access to the "cascaded" version of the attribute within
the call.

that are now affixed to _MapperConfig
- declarative now creates column copies ahead of time
so that they are ready to go for a declared_attr
- overhaul of declared_attr; memoization, cascading modifier
- A relationship set up with :class:`.declared_attr` on
a :class:`.AbstractConcreteBase` base class will now be configured
on the abstract base mapping automatically, in addition to being
set up on descendant concrete classes as usual.
fixes #2670
- The :class:`.declared_attr` construct has newly improved
behaviors and features in conjunction with declarative.  The
decorated function will now have access to the final column
copies present on the local mixin when invoked, and will also
be invoked exactly once for each mapped class, the returned result
being memoized.   A new modifier :attr:`.declared_attr.cascading`
is added as well. fixes #3150
- the original plan for #3150 has been scaled back; by copying
mixin columns up front and memoizing, we don't actually need
the "map properties later" thing.
- full docs + migration notes

distinguished for when it was actually the value ``False``.
The ``__abstract__`` flag needs to acutally evaluate to a True
value at the level being tested.
fixes #3097

mixin or abstract class when accessed, so that modifications made
to this dictionary by declarative itself won't conflict with that
of other mappings.  The dictionary is modified regarding the
``version_id_col`` and ``polymorphic_on`` arguments, replacing the
column within with the one that is officially mapped to the local
class/table. fixes #3062

- went through examples/ and cleaned out excess list() calls

become an externally usable package but still remains within the main sqlalchemy parent package.
in this system, we use kind of an ugly hack to get the noseplugin imported outside of the
"sqlalchemy" package, while still making it available within sqlalchemy for usage by
third party libraries.

between a @declared_attr Column and a
directly-defined Column on a mixin. In both
cases, the Column will be applied to the
declared class' table, but not to that of a
joined inheritance subclass.   Previously,
the directly-defined Column would be placed
on both the base and the sub table, which isn't
typically what's desired.  [ticket:2565]