fix inconsistencies in POT iterators

[zelig]

FYI there seems to be bugs in the pot iterators. Fortunately, the buggy parts don't seem to be used by anything outside the package

• Each and EachFrom return the "pinned" Val even though comment says they doen't
• Each and EachFrom report the "pinned" Val as po = 0 instead of the correct po = 256
• EachBin passes a po value to both its outer and inner iterator. The inner one seems to be unreliable.

All these POs are not well defined, i recommend we eliminate this argument from the iterator function

• Kademlia EachBin seems unnecessary and buggy Kad eachbin fix #1052