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/dynamic_numeric_diff_cost_function_test.cc

diff --git a/internal/ceres/dynamic_numeric_diff_cost_function_test.cc b/internal/ceres/dynamic_numeric_diff_cost_function_test.cc
index 19f4d88..6d1f362 100644
--- a/internal/ceres/dynamic_numeric_diff_cost_function_test.cc
+++ b/internal/ceres/dynamic_numeric_diff_cost_function_test.cc
@@ -38,6 +38,8 @@
 namespace ceres {
 namespace internal {
 
+using std::vector;
+
 const double kTolerance = 1e-6;
 
 // Takes 2 parameter blocks: