Change the type of the stats variables from uint64_t to int64_t

Some compilers complain about the printf %llx format being used with a
uint64_t
Improve the decoding for DF-11

Three changes in this one

1) Change the checksum testing for DF-11
2) Recode the Checksum generation routine to use pointers.
3) Tidy up the appearance of some print debug statments