When exiting irrelevant errors are logged

[markberger]

When receiving SIGINT, tally closes the connection with the server. Since the run loop is still executing, tally tries to get more messages from the server and receives an error. We shouldn't care about these errors because we chose to close the connection.

2013/07/29 14:32:46 Bot received os.Interrupt, exiting normally.
2013/07/29 14:32:46 Successfully sent: QUIT :
2013/07/29 14:32:46 Error reading line: 
2013/07/29 14:32:46 Error reading line: 
2013/07/29 14:32:46 Error reading line: 
2013/07/29 14:32:46 Error reading line: 
2013/07/29 14:32:46 Error reading line: 
....