Sync with forrestv/p2pool/master. delete unused branches, fix mazacoin nodes/typos 

Synced with github.com/forrestv/p2pool/master. Merges 3 PRs from there. 

Deleted all but the "fast_sha" branch (left in for experimentation) - notably, we don't need litecoin/movacoin /scrypt branches. 

Fixed a typo in the blockexplorer URL, removed no-longer-running host from BOOTSTRAP hosts list.