xo-allod: + per-type stats + pretty printing

include/xo/alloc/Object.hpp

@@ -157,6 +157,9 @@ namespace xo {
          **/
         virtual TaggedPtr self_tp() const = 0;
 
+        /** print on stream @p os **/
+        virtual void display(std::ostream & os) const = 0;
+
         // GC support
 
         /** true iff this object represents a forwarding pointer.
@@ -244,6 +247,9 @@ namespace xo {
                                   rhs.ptr());
     }
 
+    std::ostream &
+    operator<< (std::ostream & os, gp<Object> x);
+
     /** @class Cpof
      *  @brief argument to operator new used for garbage collector evacuation phase
      *