Whisper API fixed (#3687)

* whisper: wnode updated for tests with geth

* whisper: updated processing of incoming messages

* whisper: symmetric encryption updated

* whisper: filter id type changed to enhance security

* whisper: allow filter without topic for asymmetric encryption

* whisper: POW updated

* whisper: logging updated

* whisper: spellchecker update

* whisper: error handling changed

* whisper: JSON field names fixed

whisper/whisperv5/whisper_test.go

@@ -44,7 +44,7 @@ func TestWhisperBasic(t *testing.T) {
 	if uint64(w.Version()) != ProtocolVersion {
 		t.Fatalf("failed whisper Version: %v.", shh.Version)
 	}
-	if w.GetFilter(0) != nil {
+	if w.GetFilter("non-existent") != nil {
 		t.Fatalf("failed GetFilter.")
 	}
 
@@ -69,7 +69,7 @@ func TestWhisperBasic(t *testing.T) {
 	if len(mail) != 0 {
 		t.Fatalf("failed w.Envelopes().")
 	}
-	m := w.Messages(0)
+	m := w.Messages("non-existent")
 	if len(m) != 0 {
 		t.Fatalf("failed w.Messages.")
 	}