add feedback on 4 undocumented (without reason) disconnect

report from https://github.com/metajack/strophejs/pull/92

Hi,
while developing my app, I encountered several cases of "Disconnect was called because: undefined" in my logs. That wasn't very helpful and I found 4 calls of this.disconnect() without reason :

    /** Function: disconnect
     *  Start the graceful disconnection process. [...]
     *
     *  Parameters:
     *    (String) reason - The reason the disconnect is occuring.
     */

This patch adds feedback on these 4 undocumented disconnect. I hope it would be helpful to others.