unlock multiple passes and obsolete primary

* multiple passwords allowed in password file
* split on "\n", sideeffect: chop trailing slashes. fixes common mistake <(echo 'pass')
* remove accounts.Primary method
* do not fall back to primary account for mining

eth/backend.go

@@ -464,15 +464,8 @@ func (s *Ethereum) StartMining(threads int) error {
 func (s *Ethereum) Etherbase() (eb common.Address, err error) {
 	eb = s.etherbase
 	if (eb == common.Address{}) {
-		primary, err := s.accountManager.Primary()
-		if err != nil {
-			return eb, err
-		}
-		if (primary == common.Address{}) {
-			err = fmt.Errorf("no accounts found")
-			return eb, err
-		}
-		eb = primary
+		err = fmt.Errorf("no accounts found")
+		return eb, err
 	}
 	return eb, nil
 }