Add LIMIT and ORDER BY to MySQL query grammer for deletes

This addition adds LIMIT and ORDER BY to SQL generated when doing a delete when using MySQL. This is valid according to https://dev.mysql.com/doc/refman/5.0/en/delete.html. This is in reference to my origin issue report at #4040.

I submitted a pull request into master, since it changes a bit how queries are done. It shouldn't cause any issues, and should be backwards compatible, but better safe than sorry I guess. If it should go in 4.1 just let me know and I'll make another request for that.