Sweave and X11 on OSX 10.3

I see, could in this case R for the Mac be smarter about what the
default graphics device should be? This is not an Sweave issue, it
simply means that under the setup described above any call to plot()
---without actively opening a device first---will fail ...

R for the mac should probably be less smart. Since options("device") is
set at start-up there isn't much ability to tell what it should be, and we
could just use "postscript" (though "pdf" might be more appropriate on a
Mac).  We have been reluctant to special-case mac code unnecessarily, but
this does indicate a case where it might be necessary.

In the medium term this problem should go away if we get the quartz()
driver working more widely.


	-thomas