MRG: matplotlib example fix-ups and error bar colour

Which one is ROOT?

![matplotlib](https://f.cloud.github.com/assets/202816/183684/d7c8d2e8-7cac-11e2-86c8-72176666a586.png)

![ROOT](https://f.cloud.github.com/assets/202816/183679/9eec1f48-7cac-11e2-8f14-a01c3552efdc.png)

Known Issues
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* ROOT does not show error bar caps when stacking.
* ROOT does not show error bars on the markers in legends.
* ROOT and matplotlib don't play nice with each other. TCanvas locks up while a matplotlib canvas is open.