This is useful to be able to pass in mysql_limit=1 from using the
ORM.

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

a label that was anonymous, then labeled again with a name, would
fail to be locatable via a textual label.  This situation occurs
naturally when a mapped :func:`.column_property` is given an
explicit label in a query.
fixes #3340

operation with unicode parameters.  SQLAlchemy now passes both
the statement as well as the bound parameters as unicode
objects, as PyMySQL generally uses string interpolation
internally to produce the final statement, and in the case of
executemany does the "encode" step only on the final statement.
fixes #3337

the string label placed in the order_by() or group_by() of a statement
would place higher priority on the name as found
inside the FROM clause instead of a more locally available name
inside the columns clause.
fixes #3335

out.
- add __backend__ to the dialect suite so that it runs on CI.
- will be 1.0.0b3

- changelog for #2771