Need to update sqlexp to pick up MsgNotice changes

[shueybubbles]

To fix microsoft/go-sqlcmd#76 we need to pass along SQL Server-specific fields included with the information token, such as state and class.

Now that sqlexp merged golang-sql/sqlexp@d42ba59 we can implement fmt.Stringer on mssql.Error and pass an instance of it as the Message member of sqlexp.MsgNotice