[MAJOR] migrated task, tree64 and session to pool2

task and tree64 are already very close in size and are merged together.
Overall performance gained slightly by this simple change.
diff --git a/include/types/session.h b/include/types/session.h
index 7ef138f..819acfd 100644
--- a/include/types/session.h
+++ b/include/types/session.h
@@ -2,7 +2,7 @@
   include/types/session.h
   This file defines everything related to sessions.
 
-  Copyright (C) 2000-2006 Willy Tarreau - w@1wt.eu
+  Copyright (C) 2000-2007 Willy Tarreau - w@1wt.eu
   
   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
@@ -123,10 +123,6 @@
 };
 
 
-#define sizeof_session  sizeof(struct session)
-extern void **pool_session;
-
-
 #endif /* _TYPES_SESSION_H */
 
 /*