Sometimes it might be useful to have 'native' autocommit support
provided by a DB API driver rather than rely on SQLAlchemy autocommit
emulation.

format
- add an extra doc to MySQLdb
- changelog

check for 'utf8_bin' collation, as this fails on MySQL server < 5.0.
fixes #3274

and Pymysql under Python 2.   This refers to the SQL statements
themselves, not the parameters, and affects issues such as table
and column names using non-ASCII characters.   These drivers both
appear to support Python 2 Unicode objects without issue in modern
versions.
fixes #3121

sqlalchemy/orm, sqlalchemy/event, sqlalchemy/testing

to get all flake8 passing

- restore mysqldb fully within dialects/mysql/, it's no longer a connector.
fixes #2984

type such as "charset" and "collation".  While MySQL wants all character-
based CAST calls to use the CHAR type, we now create a real CHAR
object at CAST time and copy over all the parameters it has, so that
an expression like ``cast(x, mysql.TEXT(charset='utf8'))`` will
render ``CAST(t.col AS CHAR CHARACTER SET utf8)``.

- Added new "unicode returns" detection to the MySQL dialect and
to the default dialect system overall, such that any dialect
can add extra "tests" to the on-first-connect "does this DBAPI
return unicode directly?" detection. In this case, we are
adding a check specifically against the "utf8" encoding with
an explicit "utf8_bin" collation type (after checking that
this collation is available) to test for some buggy unicode
behavior observed with MySQLdb version 1.2.3.  While MySQLdb
has resolved this issue as of 1.2.4, the check here should
guard against regressions.  The change also allows the "unicode"
checks to log in the engine logs, which was not previously
the case. [ticket:2906]