lots of small changes

name_scan help corrected, typo channles, --version --help and RPC help
working, coinexplorer names added, --noirc and --notify, more
checkpoints, purge depth on first run not showing warning, more dns
seeds, coinexplorer after readBlockFile now sets persistance correctly.
typo a/e mixup

typo persist(a/e)nce -> should be with an e
using persistence with an e

easy to miss the difference by one character
Merge pull request #74 from jonasbits/tinyChanges

Thanks Jonas - took longer than anticipated - always feel free to mail me directly if I oversee a pull req for too long