only duplicated Share class so next few changes are visible
added new share class
changed new share to delay payouts 1 share
increased last_txout_nonce length from 4 to 8 bytes
use OP_RETURN in new shares
change SHARE_PERIOD and SPREAD to new values on switch to new share implementation
incremented network version to 13
store total share count and work within shares
simplified transaction preforwarding by requiring shares to be accompanied by only their _new_ transactions, instead of all the transactions they use
increased maximum difficulty multiplier to 30