CA-100400: Store the event size alongside the event in the event.next queue

Signed-off-by: Jon Ludlam <jonathan.ludlam@citrix.com>

Conflicts:
	ocaml/xapi/xapi_event.ml
CA-100400: GC event queue based on size rather than number.

Signed-off-by: Jon Ludlam <jonathan.ludlam@citrix.com>

Conflicts:
	ocaml/xapi/xapi_event.ml
Merge pull request #1933 from jonludlam/CA-100400-new-master

CA-100400