Set rounded corners for charts
*Created originally on Bitbucket by [lacoursj (Jeff LaCoursiere)](https://bitbucket.org/%7B911d7ecf-071c-4c1d-bc20-4be1b6879602%7D/)* Looking at the XML source for a chart that I manually applied rounded corners to, I just need to get <c:roundedCorners val="1"/> into the chart's XML.
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