pyodbc will no longer specify a default "driver name", and a warning
is emitted if this is missing.  The optimal driver name for SQL Server
changes frequently and is per-platform, so hostname based connections
need to specify this. DSN-based connections are preferred.
fixes #3182

statements which operate when an explicit INSERT is being
interjected into an IDENTITY column, to support non-ascii table
identifiers on drivers such as pyodbc + unix + py2k that don't
support unicode statements.
ref #3091 as this fix is also in that issue's patch, but is
a different issue.

to get all flake8 passing

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

pymysql) from working in Py3K, where a check for "connection
charset" would fail due to Py3K's more strict value comparison
rules.  The call in question  wasn't taking the database
version into account in any case as the server version was
still None at that point, so the method overall has been
simplified to rely upon connection.character_set_name().
[ticket:2933]

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]