Check and submit multiple nonces in one loop

Added to most algos, checkhash function scans a big range
and can find multiple nonces at once if the difficulty is low.

Stop ignoring them, submit second one if found...

Clean the draft code for rc=2 implemented for blake and pentablake

btw... fix the reduced displayed hashrate when a nonce is found...

Signed-off-by: Tanguy Pruvot <tanguy.pruvot@gmail.com>