Optimized and fixed some features

[lyonsdpy]

1. RPCReply struct can't get ok correctly,so I changed it to *struct{},if it's nil means ok is false
2. Add XmlnsXc attribute to rpc header(adapt to some other vendor)
3. Delete xml header encapsulation
4. Add NewSSHSessionFromClient and connToTransportFromCLientfuntion that can create session from an exist ssh.client
5. Add capabilities args in NewSession, you can send your own capabilities

[nemith]

Closed due to age.