Add Client#query_info

Hey,

It's basically a direct mapping to [mysql_info](http://dev.mysql.com/doc/refman/5.5/en/mysql-info.html). I didn't use #info, because #info is taken by mysql_client_info.

I'm using this function to get the number of skipped rows after LOAD DATA INFILE. I didn't find another way to obtain that counter. So it could be useful for somebody else.

Thanks