See [ktable_forward_hash][1]

If this comparison should make sense we need to add that to [forward_hash_no_rc][2] too, and fix it to reflect what the [C++ _hash function][3] requires.

[1]: https://github.com/ged-lab/khmer/blob/master/khmer/_khmermodule.cc#L976
[2]: https://github.com/ged-lab/khmer/blob/master/khmer/_khmermodule.cc#L4938
[3]: https://github.com/ged-lab/khmer/blob/master/lib/ktable.cc#L29