[SharpDX] Remove MathUtil.WithinEpsilon(a,b) in favor of a more accurate MathUtil.NearEqual. Replace all code performing near equal using MathUtil.ZeroTolerance with MathUtil.NearEqual. Add MathUil.IsZero/IsOne and replace all code using it. Move random functions from MathUtil to RandomUtil.
[SharpDX] Remove direct usage of MathUtil.ZeroTolerance in favor of MathUtil.IsZero
[SharpDX] Fix compilation issue on net20 target