Fix bug #314:

- remove most of the metaprogramming kung fu in MathFunctions.h (only keep functions that differs from the std)
- remove the overloads for array expression that were in the std namespace

Eigen/src/Eigenvalues/MatrixBaseEigenvalues.h

@@ -121,10 +121,11 @@ template<typename Derived>
 inline typename MatrixBase<Derived>::RealScalar
 MatrixBase<Derived>::operatorNorm() const
 {
+  using std::sqrt;
   typename Derived::PlainObject m_eval(derived());
   // FIXME if it is really guaranteed that the eigenvalues are already sorted,
   // then we don't need to compute a maxCoeff() here, comparing the 1st and last ones is enough.
-  return internal::sqrt((m_eval*m_eval.adjoint())
+  return sqrt((m_eval*m_eval.adjoint())
                  .eval()
 		 .template selfadjointView<Lower>()
 		 .eigenvalues()