move channel.cc channel.h to node directory; merge ns-3-tracing from mathieu

src/node/node.h

@@ -99,6 +99,8 @@ class NetDeviceList;
 class Ipv4;
 class Udp;
 class Arp;
+class TraceContext;
+class TraceResolver;
 
 class Node {
 public:
@@ -107,6 +109,8 @@ public:
   virtual ~Node();
   virtual Node* Copy() const = 0;// Make a copy of this node
 
+  virtual TraceResolver *CreateTraceResolver (TraceContext const &context) = 0;
+
   uint32_t GetId (void) const;
   uint32_t GetSystemId (void) const;
   void SetSystemId(uint32_t s);