Currently, one can specify the prefix length for an index
column using 'mysql_length' keyword argument when creating
an Index instance. But in case of composite indexes the
prefix length value is applied only to the last column.

Extend the existing API in way so that 'mysql_length' argument
value can be either:
    - an integer specifying the same prefix length value
      for each column of an index
    - a (column_name --> integer value) mapping specifying
      the prefix length value for each column of an index
      separately

Fixes issue #2704.

:class:`.ForeignKeyConstraint` will not render the ``DEFERRABLE`` keyword
on the MySQL dialect.  For a long time we left this in place because
a non-deferrable foreign key would act very differently than a deferrable
one, but some environments just disable FKs on MySQL, so we'll be less
opinionated here. [ticket:2721]

- went through examples/ and cleaned out excess list() calls

    String types.  When present, renders as
    COLLATE <collation>.  This to support the
    COLLATE keyword now supported by several
    databases including MySQL, SQLite, and Postgresql.
    [ticket:2276]

  - [change] The Text() type renders the length
    given to it, if a length was specified.

    accepts "fst" argument which is the new
    "fractional seconds" specifier for recent
    MySQL versions.  The datatype will interpret
    a microseconds portion received from the driver,
    however note that at this time most/all MySQL
    DBAPIs do not support returning this value.
    [ticket:2534]
- attempted to modernize the types tests in test_mysql a little, though has a long
way to go

become an externally usable package but still remains within the main sqlalchemy parent package.
in this system, we use kind of an ugly hack to get the noseplugin imported outside of the
"sqlalchemy" package, while still making it available within sqlalchemy for usage by
third party libraries.