Remove using namespace std;

For historical reasons we had a "using namespace std;" in port.h. This
is generally a bad idea. So removing it and along the way doing a bunch
of cpplint cleanup.

Change-Id: Ia125601a55ae62695e247fb0250df4c6f86c46c6

internal/ceres/block_random_access_sparse_matrix.cc

@@ -44,6 +44,11 @@
 namespace ceres {
 namespace internal {
 
+using std::make_pair;
+using std::pair;
+using std::set;
+using std::vector;
+
 BlockRandomAccessSparseMatrix::BlockRandomAccessSparseMatrix(
     const vector<int>& blocks,
     const set<pair<int, int> >& block_pairs)