Test that deferred/streaming PSGI responses work

They do in that the response is received, but it will be force-buffered
inside Catalyst::Action::FromPSGI by HTTP::Message::PSGI.
Use Catalyst::Response->from_psgi_response to support PSGI streaming responses

Deferred responses are supported, but streaming responses were
force-buffered into memory before being sent over the wire.  Using
Catalyst's method avoids this because it will return the open filehandle
to write directly to.