Log Message:
links{,-gui}: Update to 2.20.1

Changes:
2.20.1
------
- Fixed an error "ERROR: event_base_loop failed: Bad file descriptor"
  if the user quits the master instance on OpenBSD.
  OpenBSD uses an old libevent-1.4.15 and it doesn't handle calling
  event_reinit from event handler.
  libevent-2.1.11 also doesn't allow calling event_reinit from event
  handler, so it is fixed as well.