= io: test for invalid connection closure for SSL connections, refs #393

 * tests that try to more closely make sure that the messages are sent
   in proper order
 * added tests for checking that no sessions are lost by broken SSL
   closure as this is the most important consequence of wrong SSL
   closing behaviour
= io: improve SSL closing sequence, fixes #393

Changes:
  * when user wants to close connection, don't do so immediately but
    let SSLEngine drive the decision (encrypt -> CLOSED)
  * also when peer closes connection on SSL level (decrypt -> CLOSED),
    don't warn (and close underlying transport) but follow the usual
    connection closing path