TestProcess updates for rendering text with a Proc

I'm just trying to get people aware of my new patch. It's a very
simple update to TestProcess that allows testing of streaming output.
Before my patch TestProcess tries to build an HTML::Document with the
Proc instead of the captured output of the Proc. I've put this
together against tags/2.3.2.1, but I'm willing to rework it should
someone recommend I do it on a different branch.

https://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/2423-rendering-text-with-a-proc-fails-in-testing

I decided to write up a bit more of a description:
http://www.somethingunimportant.com/2009/04/06/rails-bug-found-while-streaming-output-in-actioncontroller-tests/