tests(peer) ensure String() works when p created WithId
presently, fails
fix(peer) perform bounds check on peer Id when printing String
doc(peer) add TODO

TODO ensure correctness at ID generation and enforce this by only exposing functions that generate IDs safely. Then any peer.ID type found in the codebase is known to be correct.
Merge pull request #222 from jbenet/fix/peer-string-2014-10-28

fix(peer) String() bounds check