Unified multistatus output for all REPORT outputs.

Unified multistatus output for all REPORT outputs.

"multiget" and "query" REPORTs now use the same code path for
outputing results in DAV "multi-status" format, keeping this logic
DRY.

"query" reports are currently operating through a vile sleazy hack
that makes it output every item in the calendar without applying
any filters.  That's the next piece to work on.