Prepare multiple nonces support in one loop (if found)

Tested on x11 which find sometimes 3 nonces in one call,
actually they are ignored because only the biggest was kept...

This commit doesnt fix that, but will allow to enhance shares rate later...
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>