Corrects some warnings and adds tox config.  Adds DeprecationWarning
to the error category.   Large sweep for string literals w/ backslashes
as this is common in docstrings

Co-authored-by: Andrii Soldatenko
Fixes: #3886
Change-Id: Ia7c838dfbbe70b262622ed0803d581edc736e085
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/337

Change-Id: I4e8c2aa8fe817bb2af8707410fa0201f938781de

The "raise_on_sql" option differentiates from "raise" in that
firing a lazy loader is OK as long as it does a simple
get from identity map.   Whereas "raise" is more useful
for the case that objects are to be detached.

As part of this, refactors the strategy initiation logic
a bit so that a LoaderStrategy itself knows what "key" was used
to create it, thus allowing variants of a single strategy
based on what the "lazy" argument is.  To achieve this we
have to also get rid of _get_strategy_by_cls().

Everything here is internal with the one exception of an apparently
undocumented, but not underscored, "strategy_class" key
on relationship().   Though it's not clear what
"strategy_class" accomplishes; at this point the strategy
system is extensible using Property.strategy_for().

Fixes: #3812
Change-Id: I812ad878ea5cf764e15f6f71cb39eee78a645d88

fixes #3488

Change-Id: Ic9577b800e4a4e2465ec7f3a2e95bd231f5337ee
Co-Authored-By: Mike Bayer <mike_mp@zzzcomputing.com>

primary key before emitting an INSERT, and merges distinct objects with
duplicate primary keys together as they are encountered, which is
essentially semi-deterministic at best.   This behavior
matches what happens already with persistent objects.
fixes #3601

didn't implement ``__slots__``, and therefore meant all subclasses
of that class didn't either, negating the rationale for ``__slots__``
to be in use.  Didn't cause any issue except on IronPython
which apparently does not implement ``__slots__`` behavior compatibly
with cPython.
Fixes #3494

mapped attribute on top of an :func:`.aliased` object would
resolve to the original mapper, not the :func:`.aliased`
version of it, thereby causing problems for a :class:`.Query`
that relies on this attribute (e.g. it's the only representative
attribute given in the constructor) to figure out the correct FROM
clause for the query.
fixes #3466
- apply consitency to ._parententity vs.
__clause_element__()._annotations['parententity']
in terms of aliased class, test it all.

simple but unusual system allows for a dramatic savings in Python
overhead for the construction and processing of orm :class:`.Query`
objects, from query construction up through rendering of a string
SQL statement.
fixes #3054