Thankfully, this hasn't happened in any other code yet, but it happened
while I was trying something out. Using '==' on two ByteBuffers to check
whether they're equal seemed straight-forward, so I ran into the trap.
This seems to be because ByteBuffer implements 'operator bool', and C++
considers bool to be an integer type. Thus, when trying to find a way to
evaluate '==', it attempts integer promotion, which in turn finds 'operator bool'.
This explains why all non-empty buffers seem to be equal, but different from the
empty one. Also, why comparison seems to be implemented.
