Handle cases where server resets connection

[caleblloyd]

Right now there are a few loose ends when the MySQL server resets a connection. This is mainly encountered in our tests by submitting packets over max_packet_size, described in #40

• Calls that use the connection in MySqlConnection.Dispose will fail
• Reset MySQL sessions should not be re-used by the connection pool
• If MySqlConnection.Dispose throws an exception, connections could be "checked out" of their connection pool forever (need try/finally logic with last step being to return a connection to the pool)