Make FilePermissionError derive from UIError [bug 19]
Make FilePermissionError derive from UIError [bug 19]

mixminion/mixminion,crooks/mixminion,nmathewson/mixminion,mixminion/mixminion,mixminion/mixminion,reezer/mixminion,nmathewson/mixminion,rxcomm/mixminion,Javex/mixminion,Javex/mixminion,crooks/mixminion,rxcomm/mixminion,rxcomm/mixminion,mixminion/mixminion,reezer/mixminion,Javex/mixminion,reezer/mixminion,Javex/mixminion,nmathewson/mixminion,crooks/mixminion,crooks/mixminion,rxcomm/mixminion,reezer/mixminion,nmathewson/mixminion