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

accounts/accounts_test.go

@@ -18,7 +18,7 @@ func TestSign(t *testing.T) {
 	pass := "" // not used but required by API
 	a1, err := am.NewAccount(pass)
 	toSign := randentropy.GetEntropyCSPRNG(32)
-	am.Unlock(a1.Address, "", 0)
+	am.Unlock(a1.Address, "")
 
 	_, err = am.Sign(a1, toSign)
 	if err != nil {