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

could inappropriately pull in the parent table, and also return results
inconsistent based on what's in the parent table, when the primaryjoin
includes some kind of discriminator against the parent table, such
as ``and_(parent.id == child.parent_id, parent.deleted == False)``.
While this primaryjoin doesn't make that much sense for a one-to-many,
it is slightly more common when applied to the many-to-one side, and
the one-to-many comes as a result of a backref.
Loading rows from ``child`` in this case would keep ``parent.deleted == False``
as is within the query, thereby yanking it into the FROM clause
and doing a cartesian product.  The new behavior will now substitute
the value of the local "parent.deleted" for that parameter as is
appropriate.   Though typically, a real-world app probably wants to use a
different primaryjoin for the o2m side in any case.
fixes #2948

a table has multiple, composite foreign keys targeting a parent table,
the :paramref:`.relationship.foreign_keys` argument will be properly
interpreted in order to resolve the ambiguity; previously this condition
would raise that there were multiple FK paths when in fact the
foreign_keys argument should be establishing which one is expected.
fixes #2965

- support annotations on Column where name isn't immediately present

become an externally usable package but still remains within the main sqlalchemy parent package.
in this system, we use kind of an ugly hack to get the noseplugin imported outside of the
"sqlalchemy" package, while still making it available within sqlalchemy for usage by
third party libraries.