Fix Dapper MySQLTests

[bgrainger]

Dapper includes a MySQLTests test suite.

If I change the tests to use the MySqlConnector NuGet package instead of MySql.Data, DapperEnumValue_Mysql fails with:

System.NotImplementedException : GetFieldType for Null is not implemented
   at MySql.Data.MySqlClient.Results.ResultSet.GetFieldType(Int32 ordinal)
   at MySql.Data.MySqlClient.MySqlDataReader.GetFieldType(Int32 ordinal)
   at Dapper.SqlMapper.GetColumnHash(IDataReader reader, Int32 startBound, Int32 length)
   at Dapper.SqlMapper.QueryRowImpl[T](IDbConnection cnn, Row row, CommandDefinition& command, Type effectiveType)
   at Dapper.SqlMapper.QuerySingle[T](IDbConnection cnn, String sql, Object param, IDbTransaction transaction, Nullable`1 commandTimeout, Nullable`1 commandType)
   at Dapper.Tests.Common.DapperEnumValue(IDbConnection connection)
   at Dapper.Tests.MySQLTests.DapperEnumValue_Mysql()

[bgrainger]

The failing line of code is

(AnEnum)connection.QuerySingle<int>("select @v, @y, @z", new { v = AnEnum.B, y = (AnEnum?)AnEnum.B, z = (AnEnum?)null });

Connector/NET returns VARCHAR from GetDataTypeName(2) and typeof(string) from GetFieldType(2). MySqlConnector throws a NotImplementedException in both functions.

[bgrainger]

Fixed in 0.19.4