AD values in Annotation aren't Integers

[MattWellie]

Relates to #661

This issue is better explained there - as far as I can see the AD processing script includes the possibility of generating float values for an Integer field, which causes the pysam handler to raise an exception.

1. Am I interpreting this error mode correctly? It seems like the odds of nobody ever having run into this before are wildly unlikely, but the errors I am deterministically seeing now make sense if this is a bug in the code
2. If so, can we replace this with a floor division (//) or int() wrapper so that we only ever populate ints into the Integer field