imjournal: consolidate goto labels in readjournal()
imjournal: sanitize messages as imuxsock does it

This change makes these directives available for imjournal:
  $ControlCharacterEscapePrefix
  $DropTrailingLFOnReception
  $Escape8bitCharactersOnReceive
  $EscapeControlCharacterTab
  $EscapeControlCharactersOnReceive
  $SpaceNLOnReceive