write_merge doesn't need to own the pairs iterator.  it just can take a mut reference to it.  this moves overflows_eaten out to the caller, which makes more sense anyway.
write_merge doesn't need to own the pairs iterator.  it just can take a mut reference to it.  this moves overflows_eaten out to the caller, which makes more sense anyway.

zumero/Elmo,zumero/Elmo