If you have a lot of or a few big nocow files (like vm images) which
contain a lot of potential deduplication candidates, bees becomes
incredibly slow running through a lot "invalid operation" exceptions.
Let's just skip over such files to get more bang for the buck. I did no
regression testing as this patch seems trivial (and I cannot imagine any
pitfalls either). The process progresses much faster for me now.
I got a little too enthusiastic when redacting the code, and removed some
overloaded functions bees was using. C++ silently found replacements,
and the result was a bug that prevented any data from being persisted
from the hash table.
Fixes: https://github.com/Zygo/bees/issues/7
