INSERT, either through the values clause or as a "from select",
would pollute the column types used in the result set produced by
the RETURNING clause when columns from both statements shared the
same name, leading to potential errors or mis-adaptation when
retrieving the returning rows.
fixes #3248

anonymous bound parameter names within expressions, to match the
existing use of this value as the key when rendered in an INSERT
or UPDATE statement.   This allows :attr:`.Column.key` to be used
as a "substitute" string to work around a difficult column name
that doesn't translate well into a bound parameter name.   Note that
the paramstyle is configurable on :func:`.create_engine` in any case,
and most DBAPIs today support a named and positional style.
fixes #3245

itself as a "Could not locate column" error when using
:class:`.Query` to  select from multiple, anonymous column
entities when querying against SQLite, as a side effect of the
"join rewriting" feature used by the SQLite dialect.
fixes #3241

further fixes for #3034

- add support for self-referential foreign keys to move over as well when
the table name is changed.

of the "constants" :func:`.null`, :func:`.true`, and :func:`.false`
has been reverted.   These functions returning a "singleton" object
had the effect that different instances would be treated as the
same regardless of lexical use, which in particular would impact
the rendering of the columns clause of a SELECT statement.
fixes #3170