Bug 1382: move using std::size_t/ptrdiff_t to Eigen's namespace (still better than the global namespace!)
Bug 1382: move using std::size_t/ptrdiff_t to Eigen's namespace (still better than the global namespace!)

ritsu1228/eigen,pasuka/eigen,pasuka/eigen,ritsu1228/eigen,ritsu1228/eigen,pasuka/eigen,ritsu1228/eigen,ritsu1228/eigen,pasuka/eigen,pasuka/eigen