Added ability to publish retained messages

CHANGES.txt

@@ -1,3 +1,6 @@
+1.6
+    * Added the ability to publish a retained message
+
 1.5
     * Added default constructor
     * Fixed compile error when used with arduino-0021 or later

PubSubClient.cpp

@@ -129,16 +129,22 @@ int PubSubClient::publish(char* topic, char* payload) {
    return publish(topic,(uint8_t*)payload,strlen(payload));
 }
 
-
 int PubSubClient::publish(char* topic, uint8_t* payload, uint8_t plength) {
+   return publish(topic, payload, plength, 0);
+}
+
+int PubSubClient::publish(char* topic, uint8_t* payload, uint8_t plength, uint8_t retained) {
    if (connected()) {
       uint8_t length = writeString(topic,buffer,0);
       int i;
       for (i=0;i<plength;i++) {
          buffer[length++] = payload[i];
       }
-      //header |= 1; retain
+      uint8_t header = MQTTPUBLISH;
-      write(MQTTPUBLISH,buffer,length);
+      if (retained != 0) {
+         header |= 1;
+      }
+      write(header,buffer,length);
       return 1;
    }
    return 0;

PubSubClient.h

@@ -32,6 +32,7 @@ public:
    void disconnect();
    int publish(char *, char *);
    int publish(char *, uint8_t *, uint8_t);
+   int publish(char *, uint8_t *, uint8_t, uint8_t);
    void subscribe(char *);
    int loop();
    int connected();