scenario, where an INSERT/DELETE can be turned into an UPDATE.
In this situation, a many-to-one relationship set to None, or
in some cases a scalar attribute set to None, may not be detected
as a net change in value, and therefore the UPDATE would not reset
what was on the previous row.   This is due to some as-yet
unresovled side effects of the way attribute history works in terms
of implicitly assuming None isn't really a "change" for a previously
un-set attribute.  See also :ticket:`3061`. fixes #3060

eager loads across a polymorphic-subclass boundary in conjunction
with polymorphic loading would fail to locate the subclass-link in the
chain, erroring out with a missing property name on an
:class:`.AliasedClass`. fixes #3055

Documentation fix-up: "its" vs. "it's"

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.

AttributeErrors or KeyErrors that should raise during mapper
configuration due to user errors.  The catch for attribute/keyerror
has been made more specific to not include the configuration step.
fixes #3047

Found using: https://github.com/intgr/topy

a join condition that is strictly from a single column to itself,
translated through some kind of SQL function or expression.  This
is kind of experimental, but the first proof of concept is a
"materialized path" join condition where a path string is compared
to itself using "like".   The :meth:`.Operators.like` operator has
also been added to the list of valid operators to use in a primaryjoin
condition.  fixes #3029

be used to manufacture objects that behave as though they were loaded
from a session, then detached.   Attributes that aren't present
are marked as expired, and the object can be added to a Session
where it will act like a persistent one. fix #3017