Merge branch 'maint-1.3' into maint

* maint-1.3:
  Ensure proper ordering in linking negotiation
  Add aggressive check before transfering userfile for compat
  This check doesn't work here as a separate dcc is created for transfer
  Validate sooner when the update is first offered and initiated
  Fix non-hubs being able to update other bots
  Only accept share lines from the bot sending the userfile
  Fix leaf bots being able to initiate userfile transfer to hubs
  Only validate hosts for the linking bot, not all
  Fix passing no user into user_has_host() not properly looking up user
  Enable host-user matching for bot links