Make it easier to access submitted data about fakeweb

[matthutchinson]

I can confirm this is necessary when using FakeWeb to stub requests from the RestClient gem (2.0.0+).

Without inspecting this IO stream data, there's no way to see what was sent. Since FakeWeb.last_request.body will be nil in the common case of sending a String payload with RestClient::Request.execute(...).

It is due to this code in RestClient::Request creating a RestClient::Payload::Base (or similar depending on the type of body data) and attaching it to the Net::HTTP request body_stream (rather than body).

This was documented here as a performance improvement with the release of RestClient v2.0.0

Add actual support for streaming request payloads. Previously rest-client would call .to_s even on RestClient::Payload::Streamed objects. Instead, treat any object that responds to .read as a streaming payload and pass it through to .body_stream= on the Net:HTTP object. This massively reduces the memory required for large file uploads.

This isn't an issue with Net::HTTP unless you're setting body_stream directly on the request.