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

unsupported/test/minres.cpp

@@ -7,6 +7,7 @@
 // This Source Code Form is subject to the terms of the Mozilla
 // Public License v. 2.0. If a copy of the MPL was not distributed
 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+#include <cmath>
 
 #include "../../test/sparse_solver.h"
 #include <Eigen/IterativeSolvers>