*** Current status of THREADS implementation ***

TODO (must have):
    - threads caching
    - (better) updating threaded message list on message delete and check-recent

TODO (other):
    - button in #listcontrols to mark all messages in current thread (with selected
      root or child message),
    - icons for thread tree structure

KNOWN ISSUES:
    - IE6: message, flag, attachment icons are not displayed in 
      initially collapsed child rows