sparsify - utility to punch out blocks of 0s in a file

[Ron Yorston]

OK, I tried it out for my use case of flinging VM filesystem images around
on ext4 and it seems to do the job.  I don't have any 64-bit systems
here at home so I used my feeble 32-bit netbook.  Since sizeof(off_t) !=
sizeof(long long) the debug output was all wrong:

   punching at 8989607068975104 len -4635819229210214401

but the image file and the host filesystem both survived the ordeal.

Ron