move sparse solvers from unsupported/ to main Eigen/ and remove the "not stable yet" warning

Eigen/src/SparseCore/SparseFuzzy.h

@@ -0,0 +1,41 @@
+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra.
+//
+// Copyright (C) 2008 Gael Guennebaud <gael.guennebaud@inria.fr>
+//
+// 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 EIGEN_SPARSE_FUZZY_H
+#define EIGEN_SPARSE_FUZZY_H
+
+// template<typename Derived>
+// template<typename OtherDerived>
+// bool SparseMatrixBase<Derived>::isApprox(
+//   const OtherDerived& other,
+//   typename NumTraits<Scalar>::Real prec
+// ) const
+// {
+//   const typename internal::nested<Derived,2>::type nested(derived());
+//   const typename internal::nested<OtherDerived,2>::type otherNested(other.derived());
+//   return    (nested - otherNested).cwise().abs2().sum()
+//          <= prec * prec * (std::min)(nested.cwise().abs2().sum(), otherNested.cwise().abs2().sum());
+// }
+
+#endif // EIGEN_SPARSE_FUZZY_H