d3.js: constraining drag do circular path : response to http://jsfiddle.net/EBMSr/17/

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README.md

Constraining drag/mousemove to circular path …… ? 8

Answering the question if D3 can move circles around a circular path, which included the starting point / example (http://jsfiddle.net/EBMSr/17/)

Stated a different way, this asks whether D3 can constrain a drag/move to a circular path.