big eigen2support fix, aimed at users who relied on internal eigen2 stuff: now we dont need customizations in test/eigen2/main.h anymore.

These tests already build:
eigen2_basicstuff
eigen2_adjoint
eigen2_linearstructure
eigen2_prec_inverse_4x4

Eigen/src/Eigen2Support/Meta.h

@@ -0,0 +1,39 @@
+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra.
+//
+// Copyright (C) 2011 Benoit Jacob <jacob.benoit.1@gmail.com>
+//
+// Eigen is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public
+// License as published by the Free Software Foundation; either
+// version 3 of the License, or (at your option) any later version.
+//
+// Alternatively, you can redistribute it and/or
+// modify it under the terms of the GNU General Public License as
+// published by the Free Software Foundation; either version 2 of
+// the License, or (at your option) any later version.
+//
+// Eigen is distributed in the hope that it will be useful, but WITHOUT ANY
+// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+// FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License or the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License and a copy of the GNU General Public License along with
+// Eigen. If not, see <http://www.gnu.org/licenses/>.
+
+#ifndef EIGEN2_META_H
+#define EIGEN2_META_H
+
+template<typename T>
+struct ei_traits : internal::traits<T>
+{};
+
+template<typename T, typename U>
+struct ei_is_same_type
+{
+  enum { ret = internal::is_same<T, U>::value };
+};
+
+
+#endif // EIGEN2_META_H