remove 'using namespace std' also from comments

wrap/gcache/cache.h

@@ -26,7 +26,6 @@ typedef unsigned __int64 uint64_t;
 
 #include "provider.h"
 
-//using namespace std;
 /* this cache system enforce the rule that the items in a cache are always in all the cache below */
 /* two mechanism to remove tokens from the cache:
       1) set token count to something low

wrap/gui/frustum.h

@@ -59,7 +59,6 @@ Adding copyright.
 #include <vcg/space/line3.h>
 
 #include <iostream>
-//using namespace std;
 
 namespace vcg {
 

wrap/gui/trackutils.h

@@ -35,7 +35,6 @@
 #include <wrap/gl/space.h>
 #include <vector>
 #include <iostream>
-//using namespace std;
 
 namespace vcg {