title: Calculate square root of a BigInteger (System.Numerics.BigInteger)
body: <p>.NET 4.0 provides the <code>System.Numerics.BigInteger</code> type for arbitrarily-large integers. I need to compute the square root (or a reasonable approximation -- e.g., integer square root) of a <code>BigInteger</code>. So that I don't have to reimplement the wheel, does anyone have a nice extension method for this?</p>