fixing failing test in OverlayPlotContainerTestCase
fixing failing test in OverlayPlotContainerTestCase

ContinuumIO/chaco,burnpanck/chaco,tommy-u/chaco,burnpanck/chaco,ContinuumIO/chaco,tommy-u/chaco,ContinuumIO/chaco,ContinuumIO/chaco,burnpanck/chaco,tommy-u/chaco