* adding UserLeftMusicSession (to compliment UserJoinedMusicSession)

src/client_container.proto

@@ -20,6 +20,7 @@ message ClientMessage {
 	HEARTBEAT = 107;
         FRIEND_UPDATE = 108;
         SESSION_INVITATION = 109;
+        USER_LEFT_MUSIC_SESSION = 110;
 
 	TEST_SESSION_MESSAGE = 200;
 
@@ -53,6 +54,7 @@ message ClientMessage {
     optional Heartbeat          heartbeat = 107;
     optional FriendUpdate         friend_update = 108; // from server to all friends of user
     optional SessionInvitation      session_invitation = 109; // from server to user
+    optional UserLeftMusicSession   user_left_music_session = 110;
 
     // Client-Session messages (to/from)  
     optional TestSessionMessage     test_session_message = 200;
@@ -130,6 +132,17 @@ message UserJoinedMusicSession {
     optional string username = 3; // meant to be a display name
 }
 
+// route_to: client:
+// sent by server to let the rest of the participants know a user has joined. 
+// this feels a little off; client could initiate this to other clients, right?
+message UserLeftMusicSession {
+    optional string session_id = 1; // the session ID
+    optional string user_id = 2; // this is the user_id and can be used for user unicast messages
+    optional string username = 3; // meant to be a display name
+}
+
+
+
 // route_to: session
 // a test message used by ruby-client currently.  just gives way to send out to rest of session
 message TestSessionMessage {