polar axes control

I don't think so--at least, I have not figured it out after

    > a few minutes of looking around and trying to understand how
    > things work. I think polar plotting needs quite a bit of
    > work. In particular, I suspect the lack of a "set_rmax"
    > method is not an oversight but a consequence of limitations
    > in the present implementation. I will look at it some more
    > and see if I can improve it. This might be long-term, not
    > quick.

In the next month or so I plan to spend some time fixing up the
limitations of polar, so I'll flag this and take a look at it then.