sqlalchemy/orm, sqlalchemy/event, sqlalchemy/testing

as a scalar subquery such as within an IN would receive inappropriate
substitutions from the enclosing query, if the same table were present
inside the subquery as were in the enclosing query such as in a
joined inheritance scenario.
fixes #3130

to again have the chance to veto rendering, as the naming convention
can make the decision that the name is "none" or not now.

constraint convention that includes ``constraint_name`` would
then force all :class:`.Boolean` and :class:`.Enum` types to
require names as well, as these implicitly create a
constraint, even if the ultimate target backend were one that does
not require generation of the constraint such as Postgresql.
The mechanics of naming conventions for these particular
constraints has been reorganized such that the naming
determination is done at DDL compile time, rather than at
constraint/table construction time.
fixes #3067

to get all flake8 passing

due to repeats would not correctly be rewritten in subqueries.
This would affect SELECT queries with any kind of subquery + join.
fixes #3057

:meth:`.Operators.__or__` and :meth:`.Operators.__invert__`
operator overload methods could not be overridden within a custom
:class:`.TypeEngine.Comparator` implementation.
fixes #3012

- add new FAQ for rendering SQL as a string

Removed ungrammatical apostrophes from documentation, replacing
"it's" with "its" where appropriate (but in a few cases with "it is"
when that read better).

While doing that, I also fixed a couple of minor typos etc.
as I noticed them.