PeerPicker uses ring hash to pick peers

Hello @majelbstoat, @x-ma, 

Please review the following commits I made in branch 'dpup-consistent-hash'.

ab666622e7e634627f2c0574475693c301758714 (2013-09-25 14:50:13 -0700)
PeerPicker uses ring hash to pick peers

Check list:


R=@majelbstoat
R=@x-ma