Our hacks in EvCleanup::next_tick and EvCleanup::asap were due
to the fact "closed" sockets were deferred and could not wake
up the event loop, causing certain actions to be delayed until
an event fired.
Instead, ensure we don't sleep if there are pending sockets to
close.
We can then remove most of the EvCleanup stuff
While we're at it, split out immediate timer handling into a
separate array so we don't need to deal with time calculations
for the event loop.