Reply correct error code on XEP-65 Stream rejection

this was previously erroneously changed with
197548b548 from 'forbidden' to
'not-acceptable'. We now change it back to 'forbidden'.

Also delete FileTransferNegotiator.rejectStream(StreamInitation) because
it is dead code and add some comments and javadoc.

smack-extensions/src/main/java/org/jivesoftware/smackx/bytestreams/socks5/Socks5BytestreamManager.java

@@ -703,6 +703,9 @@ public final class Socks5BytestreamManager implements BytestreamManager {
     /**
      * Responses to the given packet's sender with a XMPP error that a SOCKS5 Bytestream is not
      * accepted.
+     * <p>
+     * Specified in XEP-65 5.3.1 (Example 13)
+     * </p>
      * 
      * @param packet Packet that should be answered with a not-acceptable error
      * @throws NotConnectedException 

smack-extensions/src/main/java/org/jivesoftware/smackx/filetransfer/FileTransferManager.java

@@ -168,13 +168,25 @@ public class FileTransferManager {
 		return transfer;
 	}
 
+	/**
+	 * Reject an incoming file transfer.
+	 * <p>
+	 * Specified in XEP-95 4.2 and 3.2 Example 8
+	 * </p>
+	 * @param request
+	 * @throws NotConnectedException
+	 */
 	protected void rejectIncomingFileTransfer(FileTransferRequest request) throws NotConnectedException {
 		StreamInitiation initiation = request.getStreamInitiation();
 
 		IQ rejection = FileTransferNegotiator.createIQ(
 				initiation.getPacketID(), initiation.getFrom(), initiation
 						.getTo(), IQ.Type.ERROR);
-		rejection.setError(new XMPPError(XMPPError.Condition.not_acceptable));
+        // Reject as specified in XEP-95 4.2. Note that this is not to be confused with the Socks 5
+        // Bytestream rejection as specified in XEP-65 5.3.1 Example 13, which says that
+        // 'not-acceptable' should be returned. This is done by Smack in
+        // Socks5BytestreamManager.replyRejectPacket(IQ).
+		rejection.setError(new XMPPError(XMPPError.Condition.forbidden));
 		connection.sendPacket(rejection);
 	}
 }

smack-extensions/src/main/java/org/jivesoftware/smackx/filetransfer/FileTransferNegotiator.java

@@ -322,20 +322,6 @@ public class FileTransferNegotiator {
         }
     }
 
-    /**
-     * Reject a stream initiation request from a remote user.
-     *
-     * @param si The Stream Initiation request to reject.
-     * @throws NotConnectedException 
-     */
-    public void rejectStream(final StreamInitiation si) throws NotConnectedException {
-        XMPPError error = new XMPPError(XMPPError.Condition.forbidden, "Offer Declined");
-        IQ iqPacket = createIQ(si.getPacketID(), si.getFrom(), si.getTo(),
-                IQ.Type.ERROR);
-        iqPacket.setError(error);
-        connection.sendPacket(iqPacket);
-    }
-
     /**
      * Returns a new, unique, stream ID to identify a file transfer.
      *