Fixing bug in EscapeIdentifier for SqlServerProvider

Hi,

I am in process of evaluating various micro ORMs. So far I have tried Dapper and PetaPoco. They are both great when it comes to getting the data out, but their support for Inserts and Updates is not comprehensive. So far I like what I see with SqlFu. Before I could even use it, I had to fix EscapeIdentifier function. Please review and I hope you can merge it on to the main branch and publish on NuGet. 

Thanks,