Looking through the 11 stable 3.x buildbots (1 still running), I see 3 outcomes.
1. Windows: test seemed to run, test_idle listed in 'altered environment'.
2. Some *nix: test gave no error, test_idle lit in 'tests skipped'. I presume this means that at least one thing was skipped, not the entire idle suite.
3. Other *nix: no test failed, but the one test case setup gave the tclerror. This also includes the 'murray' machine. Yours, David?

_tkinter.create just calls Tkapp_New with the same args and the message comes from tcl/tk. I do not know if 'display name' is the same as the 'screenName' parameter or not. The doc string just says "Return a new Toplevel widget on screen SCREENNAME." Is this something to do with X11? If so, why isn't $DISPLAY set? Passing screenName='fake' has no effect on my Win7 machine.

I think the following patch should quiet things for now, even if not the best patch.