fix Chaco2PlotItem bug where plot always auto-scales when data is updates
fix Chaco2PlotItem bug where plot always auto-scales when data is updates

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