Updated to reference DeveloperForce.Commom 0.2.6

Updated references in packages.config.
Updated SalesforceHttpClient to ServiceHttpClient in ChatterClient.cs.
Updated AuthClient to AuthenticationClient and AuthenticatePassword to
UsernamePassword in ChatterClientTests.cs
Merge pull request #1 from DelmerJohnson/master

Updated to reference DeveloperForce.Commom 0.2.6