BRoster: whitespace
BRoster: small doc fix
BRoster: Remove brief desc comments

As per discussion, you'll just have to look in the Haiku Book for this.
Thanks Axel
Debugger: Improvements to hrev47421.

- Isolate the filesystem query/result list building into a separate
  worker thread in order to prevent blocking the window thread in
  case the query winds up being a bit more time consuming. This
  doesn't yet handle intelligent prefetching (and associated can of
  synchronization worms), but that will come once time permits.
- Also fixes a missing break statement introduced in the aforementioned
  commit, though that one shouldn't have caused any actual harm.