lp_load and lp_dump uses Python's bz2

Changed the default behavior of lp_load and lp_dump to write to compressed file objects.  Also changed the lp_load and lp_dump function arguments - now they take a file name instead of a file object.  

This allows us to delete all external calls to bunzip, bzip and so on.  Also saves a lot of space with transmitting `forcebalance.p`.