logging, exception, and  ``repr()`` purposes now truncate very large
scalar values within each collection, including an
"N characters truncated"
notation, similar to how the display for large multiple-parameter sets
are themselves truncated.
fixes #2837

to the new MutableList and MutableSet classes, fixes #3297

here, fixes #3652

from https://bitbucket.org/zzzeek/sqlalchemy/issues/3297

primary key that has values for some but not all of the PK fields
would emit a SELECT statement leaking the internal NEVER_SET symbol
into the query, rather than detecting that this object does not have
a searchable primary key and no SELECT should be emitted.
fixes #3647

INSERT, UPDATE, and DELETE statements to both specify their own
WITH clause, as well as for these statements themselves to be
CTE expressions when they include a RETURNING clause.
fixes #2551

that this structure is only intended to track additions
and removals from the dictionary, not recursive tracking
of embedded changes.  fixes #3646.