Switch the main calendar item fetching to the new logic. This
should improve resource leakage and also error handling.

The "resolution" process for Attendees has the same concepts
as before, but consistently uses a bigger set of properties
to avoid the dreaded re-resolution if ResolveNames() fails.
In any event, the re-resolution now plays dumb-but-safe - the
older logic seemed to get confused especially by non-people
attendees (i.e. resources). This may need further work.Z