Proper FIX logout sequence

[bhaan]

Changes proposed in this pull request:

• Updates acceptor/initiator stop sequence. Sends a Logout and waits for a response before invoking the application OnLogout callback, per FIX standard
• Removes redundant calls to the application OnLogout callback. Currently, the run() function in session ultimately invokes OnLogout when it returns, while the inSession state has a few cases where it invokes the callback as well.
• Improves the event log output for the logon and logout sequences. Following the QuickFIX/C++ implementation, a proper session event sequence will look like the following:

Initiator

2016/06/30 15:31:45.167656 Sending logon request
2016/06/30 15:31:45.185684 Received logon response
2016/06/30 15:31:49.810696 Inititated logout request
2016/06/30 15:31:49.825808 Received logout response
2016/06/30 15:31:49.825833 Disconnected

Acceptor

2016/06/30 15:31:45.170768 Received logon request
2016/06/30 15:31:45.182621 Responding to logon request
2016/06/30 15:31:49.814847 Received logout request
2016/06/30 15:31:49.815776 Sending logout response
2016/06/30 15:31:49.827149 Disconnected

[cbusbey]

For clarity, might be better to return immediately if err!=nil and avoid the else clause

[bhaan]

sounds good to me: 9075d98

[cbusbey]

🎂 🐙