Free rotation of Chaco plots

Using the following snippet crashes python with a fatal error
"Fatal Python error: This thread state must be current when releasing"

```
class RotatingContainer(OverlayPlotContainer):
rotation = Float(45)
use_backbuffer = False
def draw(self, gc, *args, **kw):
with gc:
w2 = self.width / 2
h2 = self.height / 2
gc.translate_ctm(w2, h2)
gc.rotate_ctm(math.radians(self.rotation))
gc.translate_ctm(-w2, -h2 - 100)
OverlayPlotContainer.draw(self, gc, *args, **kw)
```

setting use_backbuffer=True works for some cases. see "Free rotation of Chaco plots" thread in enthought mailing list

Canopy 1.0 Mac OSX 10.7.5