binaryfusefilter cannot handle some sets of large, duplicate keys #30

My understanding is that after #22 duplicate keys should be supported in binary fuse filters. I am working with uint64 keys that are CRC64 checksums (so quite large numbers) and am regularly finding sets that result in:

Unexpected error: too many iterations, you probably have duplicate keys

I've managed to reduce one such set down to just 121 keys, I will send a PR to add a test for this. Is it possible to fix this, or are there limitations to the duplicate key checking in some way?