Added isJoined method (SMACK-86)

git-svn-id: http://svn.igniterealtime.org/svn/repos/smack/trunk@2094 b35dd754-fafc-0310-a699-88a17e54d16e

source/org/jivesoftware/smack/GroupChat.java

@@ -148,6 +148,16 @@ public class GroupChat {
         join(nickname, 5000);
     }
 
+    /**
+     * Returns true if currently in the group chat (after calling the {@link
+     * #join(String)} method.
+     *
+     * @return true if currently in the group chat room.
+     */
+    public boolean isJoined() {
+        return joined;
+    }
+
     /**
      * Joins the chat room using the specified nickname. If already joined as
      * another nickname, will leave as that name first before joining under the new