re-enable NX distribution, disable basic_stats threading
re-enable NX distribution, disable basic_stats threading

now that orf_length is inline C, basic_stats is extremely fast,
so I've re-enabled NX distribution because most people will
expect to see it, and removed the threading as it is incompatible
with NX calculation. TODO: tidy up the thread disabling.


Former-commit-id: 08dc4f182578687e4b41d1be064adfeb9c032128
cboursnell/transrate,roryk/transrate,Blahah/transrate,cboursnell/transrate,roryk/transrate,roryk/transrate,Blahah/transrate,cboursnell/transrate,Blahah/transrate