fixes #3095, #3292
- reorganize enum constructor to again work with the MySQL
ENUM type
- add a new create_constraint flag to Enum to complement that of
Boolean
- reinstate the CHECK constraint tests for enum, these already
fail /skip against the MySQL backend
- simplify lookup rules in Enum, have them apply to all varieties
of Enum equally

- test_query isn't assertscompiledsql

such that we no longer assume the "ALGORITHM" keyword is present in
the reflected view source, as some users have reported this not being
present in some Amazon RDS environments.
fixes #3613

- add version switch for backend fsp test

(cherry picked from commit 67b22cee3ab2c17b61100f1ccd69081082c0f074)

an issue with just one test

of the :class:`.mysql.DATETIME`, :class:`.mysql.TIMESTAMP` and
:class:`.mysql.TIME` types would be incorrectly placed into the
``timestamp`` attribute, which is unused by MySQL, instead of the
``fsp`` attribute.
fixes #3602

individual categories w/ modernized fixtures, assert attributes
within type objects.

"auto increment" column has been changed, such that autoincrement
is no longer implicitly enabled for a :class:`.Table` that has a
composite primary key.  In order to accommodate being able to enable
autoincrement for a composite PK member column while at the same time
maintaining SQLAlchemy's long standing behavior of enabling
implicit autoincrement for a single integer primary key, a third
state has been added to the :paramref:`.Column.autoincrement` parameter
``"auto"``, which is now the default. fixes #3216
- The MySQL dialect no longer generates an extra "KEY" directive when
generating CREATE TABLE DDL for a table using InnoDB with a
composite primary key with AUTO_INCREMENT on a column that isn't the
first column;  to overcome InnoDB's limitation here, the PRIMARY KEY
constraint is now generated with the AUTO_INCREMENT column placed
first in the list of columns.