= io: register for OP_CONNECT only after the connection attempt was made, fixes #437

This is necessary because of at least two bugs in the JDK:
 * a channel is always connectable before the connection is attempted,
   and selecting for OP_CONNECT will instantly report connectable
 * even worse: after OP_CONNECT was reported true, also `finishConnect`
   will always return true, even if the connection wasn't yet established