Do not encode number of constraints. As discovered when using thrussh in tandem with ssh-agent, when trying to add a key with constraints it would fail to parse on the ssh-agent. It was discovered that this was due to the length of the constraints being encoded. Instead of doing this we simply push them onto the buffer since they are the last thing to go onto the buffer. On the server side, it simply reads the constraints until it reaches the end. It was also discovered that the server code never added the constraints to the KeyStore. This is also rectified in this patch.