Incorporate tests from dune-fufem

dune/matrix-vector/CMakeLists.txt

+add_subdirectory(test)
+
 #install headers
 install(FILES
   addtodiagonal.hh

dune/matrix-vector/test/CMakeLists.txt

+dune_add_test(SOURCES arithmetictest.cc)
+dune_add_test(SOURCES staticmatrixtoolstest.cc)

dune/matrix-vector/test/common.hh

+#ifndef DUNE_MATRIX_VECTOR_TEST_COMMON_HH
+#define DUNE_MATRIX_VECTOR_TEST_COMMON_HH
+
+template <typename FT>
+struct ToleranceTraits {
+  static constexpr FT tol = 50 * std::numeric_limits<FT>::epsilon();
+};
+
+template <class T>
+typename Dune::FieldTraits<typename T::field_type>::real_type diffDune(
+    T t1, const T& t2) {
+  t1 -= t2;
+  return t1.infinity_norm();
+}
+template <class TX>
+bool isCloseDune(TX t1, const TX& t2) {
+  return diffDune(t1, t2) < ToleranceTraits<typename TX::field_type>::tol;
+}
+template <class FT, class Other>
+bool isCloseAbs(FT t1, Other t2) {
+  return std::abs<FT>(t1 - t2) < ToleranceTraits<FT>::tol;
+}
+
+#endif