make a lot of the same changes as to fs.py for checkpointing.
make a lot of the same changes as to fs.py for checkpointing.

1) rearrange the options to be in a nice logical order
2) add an option for what i call "standard switch", which is from simple->timing->detailed
3) make checkpointing code such that checkpoints taken from the command line override checkpoint instructions compiled into binaries.
4) add an option for maximum number of checkpoints - simulation will stop at max or maxtick, whichever is first

vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5,hoangt/tpzsimul.gem5,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5,hoangt/tpzsimul.gem5,pombredanne/http-repo.gem5.org-gem5-,hoangt/tpzsimul.gem5,vovojh/gem5,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5,hoangt/tpzsimul.gem5,hoangt/tpzsimul.gem5,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5,hoangt/tpzsimul.gem5,hoangt/tpzsimul.gem5,pombredanne/http-repo.gem5.org-gem5-,vovojh/gem5