Stratum: Avoid putting new targets on pool stratum_work until mining.notify is received for it
Stratum: Keep nonce1 and n2size in a "staging" state until mining.notify is received
Stratum: Implement mining.set_extranonce, and advertise support for it to pools with a #xnsub flag
Stratum: Ignore response from mining.extranonce.subscribe
Merge branch 'nicehash' into bfgminer