- The "auto-attach" feature of constraints such as :class:`.UniqueConstraint`

- The "auto-attach" feature of constraints such as :class:`.UniqueConstraint`
and :class:`.CheckConstraint` has been further enhanced such that
when the constraint is associated with non-table-bound :class:`.Column`
objects, the constraint will set up event listeners with the
columns themselves such that the constraint auto attaches at the
same time the columns are associated with the table.  This in particular
helps in some edge cases in declarative but is also of general use.
fixes #3341