Remove 'using namespace std' from SerialTypes.h

This unfortunately cuases a ton of flow-down changes because a lot of other
code was depending on that definition existing. This has a fairly large chance
to break builds of external plugins, considering how many internal ones it broke.

src/plugin/Manager.cc

@@ -17,6 +17,7 @@
 #include "../util.h"
 #include "../input.h"
 
+using namespace std;
 using namespace plugin;
 
 Plugin* Manager::current_plugin = 0;