checksums issues between Python and C

[walchko]

I am creating yivopkt_t in C, but then I get errors in python when I read some of them. Tyically the invalid checksums are always 0 or 13 which seems strange.

I think there is an issue between the number of bits in C and python. I need to take more care and make sure I am limiting the checksum to only uint8_t in both languages. It is easy in C, but I think python is using 64-bit integers instead of 8-bit integers.