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
diff --git a/internal/ceres/line_search_direction.cc b/internal/ceres/line_search_direction.cc
index dddcecd..2d86c22 100644
--- a/internal/ceres/line_search_direction.cc
+++ b/internal/ceres/line_search_direction.cc
@@ -86,7 +86,7 @@
       LOG(WARNING) << "Restarting non-linear conjugate gradients: "
                    << directional_derivative;
       *search_direction = -current.gradient;
-    };
+    }
 
     return true;
   }