Add ViewModelWhenAnyValueDynamic to save a call to Reflection.ExpressionToPropertyNames.

Make this.OneWayBind(x => x, ...) bindings work, fixes #331.

Remove unused directive for Silverlight.
Merge pull request #354 from reactiveui/viewmodel-binding-fixes

Make this.OneWayBind(x => x, ...) bindings work (#331).