CSV System output return type

[Mattamorphic]

As a user I might want to stream out the content of the system stream, either as a new input, or to a file.

We can't use stream_get_contents() as that will dump the entire contents of the temp_file into memory - which will explode. So we should return the system object, still open and reset.

We can then do what we want (either use the generator to get the lines or pump this back into a processor)