[orca-list] More event flood detection added to Orca master

[Joanmarie Diggs <jdiggs igalia com>]

Hey all.

The problem with matrix.org is that we are getting bombarded with an
insane amount of accessible events. So I've just added a change to Orca
to try to detect this condition and skip old events flooding in from the
same object. The change is meant to be fairly conservative (read
"safe"), so you won't see the problem simply vanish. But events from the
flood are now being processed significantly faster than before.

I'll keep working on other ways to make these sorts of sites less of a
pain. In the meantime, please test master.

Thanks!
--joanie