updated Linq to Sql IUpdatable implementation

Based on feedback from Robert Fonseca-Ensor, I have made a bunch of bug and performance fixes to the IUpdatable implementation for Linq to Sql and posted those to code gallery.  Rob is also now my first official contributor to the project.

As part of ADO.NET Data Services v1.5 we have provided a new way to plug in data sources that provides the following features sorely missing from v1:

1)  Does not require the data provider to provider CLR types representing the entities exposed by the data source.  This meta data can be provided dynamically at runtime (or even per query) via a new metadata interface and does not require any static typed entities.

2)  Provides a much cleaner way for third party provider writers to write and ship stand alone ADO.NET Data Service providers.  (No more partial classes like my Linq to Sql IUpdatable implementation).

In the coming days I will posting a walk through for converting the Linq to Sql IUpdateable implementation to a full blown Linq to Sql provider for ADO.NET Data Services to demonstrate the new interface.