catch Mysql2::Errors

Closes #8

LGTM given by: @hampei

Squashed commit of the following:

commit e77b54319b68326459dd58aabf87933a5a3ede0d
Author: Samuel Esposito <s.esposito@roqua.nl>
Date:   Tue Jun 17 11:41:13 2014 +0200

    catch Mysql2::Errors