Fixed bug where declarative would not update the state of the
:class:`.Mapper` as far as what attributes were present, when additional
attributes were added or removed after the mapper attribute collections had
already been called and memoized.  Addtionally, a ``NotImplementedError``
is now raised if a fully mapped attribute (e.g. column, relationship, etc.)
is deleted from a class that is currently mapped, since the mapper will not
function correctly if the attribute has been removed.

Change-Id: Idaca8e0237b31aa1d6564d94c3a179d7dc6b5df9
Fixes: #4133

Added new attribute :attr:`.Query.lazy_loaded_from` which is populated
with an :class:`.InstanceState` that is using this :class:`.Query` in
order to lazy load a relationship.  The rationale for this is that
it serves as a hint for the horizontal sharding feature to use, such that
the identity token of the state can be used as the default identity token
to use for the query within id_chooser().

Also repaired an issue in the :meth:`.Result.with_post_criteria`
method added in I899808734458e25a023142c2c5bb37cbed869479
for :ticket:`4128` where the "unbake subquery loaders" version was calling
the post crtieria functions given the :class:`.Result` as the argument
rather than applying them to the :class:`.Query`.

Change-Id: I3c0919ce7fd151b80fe2f9b5f99f60df31c2d73d
Fixes: #4243

Fixed a race condition which could occur if automap
:meth:`.AutomapBase.prepare` were used within a multi-threaded context
against other threads which  may call :func:`.configure_mappers` as a
result of use of other mappers.  The unfinished mapping work of automap
is particularly sensitive to being pulled in by a
:func:`.configure_mappers` step leading to errors.

Change-Id: I6d36df6639bf5cb8f137187dff68f386f5e84f88
Fixes: #4266

Updated the dogpile.caching example to include new structures that
accommodate for the "baked" query system, which is used by default within
lazy loaders and some eager relationship loaders. The dogpile.caching
"relationship_caching" and "advanced" examples were also broken due to
:ticket:`4256`.  The issue here is also worked-around by the fix in
:ticket:`4128`.

Note that this recipe requires
I3f86fcb12a6a9a89aa308b335e75c25969bcc30e in order for the
"advanced" example to work.

Change-Id: I9d35417f1d6c1906555583b8225d3da7f81736f7
Fixes: #4258

The horizontal sharding extension now makes use of the identity token
added to ORM identity keys as part of :ticket:`4137`, when an object
refresh or column-based deferred load or unexpiration operation occurs.
Since we know the "shard" that the object originated from, we make
use of this value when refreshing, thereby avoiding queries against
other shards that don't match this object's identity in any case.

Change-Id: Ib91637a65d94ace7405998b8410d62944a83f2eb
Fixes: #4247

Fixed regression in 1.2 within sharded query feature where the
new "identity_token" element was not being correctly considered within
the scope of a lazy load operation, when searching the identity map
for a related many-to-one element.   The new behavior will allow for
making use of the "id_chooser" in order to determine the best identity
key to retrieve from the identity map.  In order to achieve this, some
refactoring of 1.2's "identity_token" approach has made some slight changes
to the implementation of ``ShardedQuery`` which should be noted for other
derivations of this class.

Change-Id: I04fa60535deec2d0cdec89f602935dfebeb9eb9d
Fixes: #4228

Removed a warning that would be emitted when calling upon
``__table_args__``, ``__mapper_args__`` as named with a ``@declared_attr``
method, when called from a non-mapped declarative mixin.  Calling these
directly is documented as the approach to use when one is overidding one
of these methods on a mapped class.  The warning still emits for regular
attribute names.

Change-Id: Iae7ed0bd625a2c163c910aa777cef4779128580a
Fixes: #4221

Fixed bug where using :meth:`.Mutable.associate_with` or
:meth:`.Mutable.as_mutable` in conjunction with a class that has non-
primary mappers set up with alternatively-named attributes would produce an
attribute error.  Since non-primary mappers are not used for persistence,
the mutable extension now excludes non-primary mappers from its
instrumentation steps.

Change-Id: I2630d9f771a171aece03181ccf9159885f68f25e
Fixes: #4215

Fixed a long-standing regression that occurred in version
1.0, which prevented the use of a custom :class:`.MapperOption`
that alters the _params of a :class:`.Query` object for a
lazy load, since the lazy loader itself would overwrite those
parameters.   This applies to the "temporal range" example
on the wiki.  Note however that the
:meth:`.Query.populate_existing` method is now required in
order to rewrite the mapper options associated with an object
already loaded in the identity map.  Also, a custom defined
:class:`.MapperOption` will now cause lazy loaders related to
the target object to use a non-baked query by default unless
the :meth:`.MapperOption._generate_cache_key` method is implemented.

Fixed bug where the new :meth:`.baked.Result.with_post_criteria`
method would not interact with a subquery-eager loader correctly,
in that the "post criteria" would not be applied to embedded
subquery eager loaders.   This is related to :ticket:`4128` in that
the post criteria feature is now used by the lazy loader.

Change-Id: I899808734458e25a023142c2c5bb37cbed869479
Fixes: #4128

Repaired regression caused in 1.2.3 and 1.1.16 regarding association proxy
objects, revising the approach to :ticket:`4185` when calculating the
"owning class" of an association proxy to default to choosing the current
class if the proxy object is not directly associated with a mapped class,
such as a mixin.

Change-Id: I87d0ac09f695dc285bd4bbe0a547f1d5ce23e068
Fixes: #4185