Removed the warnings that are emitted when the LRU caches employed
by the mapper as well as loader srtategies reach their threshold; the
purpose of this warning was at first a guard against excess cache keys
being generated but became basically a check on the "creating many
engines" antipattern.   While this is still an antipattern, the presense
of test suites which both create an engine per test as well as raise
on all warnings will be an inconvenience; it should not be critical
that such test suites change their architecture just for this warning
(though engine-per-test suite is always better).

Change-Id: I41ef8cd642d05a845f53119b196440f9d7879cd9
Fixes: #4071

Fixed issue where adding additional non-entity columns to
a query that includes an entity with subqueryload relationships
would fail, due to an inspection added in 1.1.11 as a result of
:ticket:`4011`.

Change-Id: I8ef082be649125bdc07b428cb9b0a77a65d73671
Fixes: #4033

The attributeimpl for a deferred_expression does not
support a scalar loader, add new configurability so that
the impl can have this flag turned off.   Document
that the with_expression() system currently does not
offer any deferred loading.

To eliminate confusion over "deferred", which refers to
lazy loading of column attributes, and "with_expression",
which refers to an attribute that is explicitly at
query time only, rename deferred_expression to query_expression.

Change-Id: I07c4a050ed68c79ccbde9492e9de1630b7470d74

Added a new feature :func:`.orm.with_expression` that allows an ad-hoc
SQL expression to be added to a specific entity in a query at result
time.  This is an alternative to the SQL expression being delivered as
a separate element in the result tuple.

Change-Id: Id8c479f7489fb02e09427837c59d1eabb2a6c014
Fixes: #3058

Instead of checking that the "orig_entity" we receive applies
as a correct FROM element for the subquery we're building,
set the FROM clause of the query to exactly what it already
is based on column_descriptions (assuming there is no FROM
list already), thereby ensuring that the FROM list will remain
intact, regardless of what orig_entity turns out to be and
what the target_cols ultimately refer towards.

Fixed issue with subquery eagerloading which continues on from
the series of issues fixed in :ticket:`2699`, :ticket:`3106`,
:ticket:`3893` involving that the "subquery" contains the correct
FROM clause when beginning from a joined inheritance subclass
and then subquery eager loading onto a relationship from
the base class, while the query also includes criteria against
the subclass. The fix in the previous tickets did not accommodate
for additional subqueryload operations loading more deeply from
the first level, so the fix has been further generalized.

Change-Id: Ic909590814f71e577d8266b1dbc4c393dc48e019
Fixes: #4011

Added a new style of mapper-level inheritance loading
"polymorphic selectin".  This style of loading
emits queries for each subclass in an inheritance
hierarchy subsequent to the load of the base
object type, using IN to specify the desired
primary key values.

Fixes: #3948

Change-Id: I59e071c6142354a3f95730046e3dcdfc0e2c4de5

level cache
- include SelectinLoader itself in the cache key, though
this is currently not critical

Change-Id: I8e4bcd579277fbe53d9c7eca3552a0b8ab9d7a39

a with_polymorphic, regardless of inheritance type, represents
multiple classes.  A subclass that wants to joinedload with innerjoin=True
needs to be demoted to an outerjoin because the parent entity rows
might not be of that type.   Looks more intuitive with a joined
inheritance load, but applies just as well to single or concrete.

Change-Id: I4d3d76106ae20032269f8848aad70a8e2f9422f9
Fixes: #3988

otherwise, it fails if you import from ext before orm:

    from sqlalchemy import *
    from sqlalchemy.ext.declarative import declarative_base
    from sqlalchemy.orm import *

and then do a lazyload, as the ext.baked importlater is not
initialized.

Change-Id: I24dcbfc9ca9022316da28507772562833e45dd95

Adding a new kind of relationship loader that is
a cross between the "immediateload" and the "subquery"
eager loader, using an IN criteria to load related items
in bulk immediately after the lead query result is loaded.

Change-Id: If13713fba9b465865aef8fd50b5b6b977fe3ef7d
Fixes: #3944