add --miner-share-rate and --address-share-rate
add --min-difficulty
round auto difficulty to power of 2
accept min diff less than one and round correctly
alt target-difficulty conversion with modifier
Merge branch 'alt-diff' into auto-worker-diff
use target/diff conversion with modifier
Merge branch 'auto-worker-diff' of https://github.com/iongchun/p2pool

Conflicts:
	p2pool/web.py