fileobject with Agg

Hi All, I'm striving to understand how I ca stuff a file

    > object (e.g. StringIO) to print_figure for an Agg backend.
    > states : "If filename is a fileobject, write
    > png to file object (thus you can, for example, write the png
    > to stdout".

This has come up a number of times. I worked on this once. The
sticking point is that libpng takes a FILE pointer, and the cstringio
doesn't provide one. There must be a way to do it, but I haven't
figured it out yet. Please file a support request on the sf site to
remind us to figure it out!