util: update checkpoint aggregation script
The checkpoint aggregation script had become outdated due to numerous changes
to checkpoints over the past couple of years. This updates the script. It
now supports aggregation for x86 architecture instead of alpha. Also a couple
of new options have been added that specify the size of the memory file to be
created and whether or not the memory file should be compressed.

util: update aggregator to handle x86 checkpoints.
Also, make update to understand some of the newer serialized variables

utils: checkpoint aggregator: some physmem files are too big to read at once,
break it up into reading one page at a time. Also, avoid redoing a aggregating a checkpoint that's
already done.