extend and cleanup use of closesocket()

- add missing closesocket() calls for BindListenPort()
- always call closesocket() before printing any text (ensure consistent
  usage in the code)

misc small changes in net:
- remove unused CNode::Cleanup()
- add missing vhListenSocket.clear() to ~CNetCleanup()

changes in ConnectSocketDirectly() unrelated to closesocket():
- replace 3 following calls to WSAGetLastError() by storing result into
  nErr and use this in an if-clause
- convert an if() to an else if(), which removes an unneded check if the
  first case is true