MySQL backend fixes for Python 3. With Python 2, text sent to and from MySQL is treated as bytes in Python. The database may be recorded by MySQL as having some other encoding (latin1 being the default in some MySQL versions - Roundup does not set an encoding explicitly, unlike in back_postgresql), but as long as MySQL's notion of the connection encoding agrees with its notion of the database encoding, no conversions actually take place and the bytes are stored and returned as-is. With Python 3, text sent to and from MySQL is treated as Python Unicode strings. When the database and connection encoding is latin1, that means the bytes stored in the database under Python 2 are interpreted as latin1 and converted from that to Unicode, producing incorrect results for any non-ASCII characters; furthermore, if trying to store new non-ASCII data in the database under Python 3, any non-latin1 characters produce errors. This patch arranges for both the connection and database character sets to be UTF-8 when using Python 3, and documents a need to export and import the database when moving from Python 2 to Python 3 with this backend.