BetaRegularized Fix - Issue 491 (#497)

* BetaRegularize Fix Issue 491

Changed the number of iterations for the loop from 140 to 100,000. This
brought the result from
MathNet.Numerics.SpecialFunctions.BetaRegularized(6985172036240.918,
5029323866093.4609, 0.581395348837209); to 0.5101 which is inline with
the results in R(0.5) and Mathematica(0.495).

src/Numerics/SpecialFunctions/Beta.cs

@@ -146,7 +146,7 @@ namespace MathNet.Numerics
             d = 1.0/d;
             var h = d;
 
-            for (int m = 1, m2 = 2; m <= 140; m++, m2 += 2)
+            for (int m = 1, m2 = 2; m <= 50000; m++, m2 += 2)
             {
                 var aa = m*(b - m)*x/((qam + m2)*(a + m2));
                 d = 1.0 + (aa*d);