Fix for Codeplex-2103 - Batch's inner request's Url not being decoded in
WebHost scenarios

The issue here is that when we do batching in a Web Host scenario, we
delegate to the System.Web route table - we do this by wrapping each
HttpRequestMessage in a wrapper that implements HttpRequestBase.

Our adapter isn't doing the right thing with respect to escaping. This
change brings the adapter into compliance and adds an integration test.