This trim race is (as far as I can tell) fine -- I see no correctness
problem with CORFU, on the client side or the server side. However,
this race with a trim causes a model problem that I believe can be
solved this way:
1. We must keep track of the fact that the page write is happening:
someone can notice the write via read-repair or even a regular read by
the tail. We do this in basically the way that all other writes
are handled in the ValuesR relation.
2. Add new code to client-side writer: if there's a trim race, *and*
if we're using PULSE, then return a special error code that says that
the write was ok *and* that we raced with trim.
2b. If we aren't using pulse, just return {ok, LPN}.
3. For the transition check property, treat the new return code as if
it is a w_tt. Actually, we use a special marker atom, w_special_trimmed
for that purpose, but it is later treated the same way that w_tt is by the
filter_transition_trimfill_suffixes() filter.
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