Consider bundling like PIECE messages

[jlouis]

Right now, every piece message will induce a message-traverse through the whole system. That means messaging for each 16KB we get in. I'd rather want to gather up PIECE messages if they can be seen as a bundle.

A bundle is a set of successive chunks. They are easy to detect. Several advantages are possible with this optimization: There is less work to do and when there is work to do we can scatter-gather process it in one fell swoop.