util: make a generic checkpoint aggregator that can aggregate different cpts into one multi-programmed cpt. Make minor changes to serialization/unserialization to get it to work properly. Note that checkpoints were made with a comment at the beginning with // - this must be changed to ## to work properly with the python config parser in the aggregator.

src/sim/serialize.cc

@@ -422,7 +422,7 @@ Serializable::serializeAll(const string &cpt_dir)
     time_t t = time(NULL);
     if (!outstream.is_open())
         fatal("Unable to open file %s for writing\n", cpt_file.c_str());
-    outstream << "// checkpoint generated: " << ctime(&t);
+    outstream << "## checkpoint generated: " << ctime(&t);
 
     globals.serialize(outstream);
     SimObject::serializeAll(outstream);