Make default character set consistent

[olafz]

In MariaEx, the default character set defaults to utf8. However, the initial client negotiation (the first client response after the server greeting) is currently hardcoded at character set 8 (which is latin1 COLLATE latin1_swedish_ci):

To make the behaviour of MariaEx consistent, this PR changes the initial client negotiation to character set 33 (which is utf8 COLLATE utf8_general_ci).

[coveralls]

Coverage decreased (-2.1%) to 82.895% when pulling caa1ec6 on olafz:master into 78cd8a7 on xerions:master.

[olafz]

The behaviour of this change has no effect on everything issued after the SET CHARACTER SET ..., which is usually the first thing that happens after the handshake:

mariaex/lib/mariaex/protocol.ex

Lines 219 to 221 in 5ef4656

	defp handle_handshake(packet(msg: ok_resp(affected_rows: _affected_rows, last_insert_id: _last_insert_id) = _packet), nil, state) do
	statement = "SET CHARACTER SET " <> (state.opts[:charset] || "utf8")
	query = %Query{type: :text, statement: statement}

[foeken]

Setting the actual proper default charset is quite a challenge since you need the internal charset nr (which is some rune from a generated IndexFile on the server side and is version specific):

Character set and collation information are specific to a server version and installation, and are generated automatically from the sql/share/charsets/Index.xml file in the source distribution.

https://github.com/mysql/mysql-server/blob/4f1d7cf5fcb11a3f84cff27e37100d7295e7d5ca/mysys/charset.cc#L629

Setting it to UTF-8 is not the true solution, perhaps this just needs to be 'known' by users of MariaEX: you need to specify an explicit charset else you will get the hard coded default not the database default. cc @michalmuskala @josevalim

Perhaps a warning/exception would be in order in those places.