Improved ASP.NET Ado MySql performance by 15-30%

As discussed in #315, this removes CommandBehavior.SingleRow which was causing extra MySql network traffic. It improved ado/mysql performance by about 15% and ado/mysql/update by about 30%. It didn't seem to affect PostgreSQL performance.

I'm not totally sure if this is an ok change to make, I welcome feedback from @pdonald and others. Thanks.