COPYable logs status

[summarising discussion on -patches]

The situation with this patch is that I now have it in a state where I
think it could be applied, but there is one blocker, namely that we do
not have a way of preventing the interleaving of log messages from
different backends, which leads to garbled logs. This is an existing
issue about which we have had complaints, but it becomes critical for a
facility the whole purpose of which is to provide logs in a format
guaranteed to work with our COPY command.

Unfortunately, there is no solution in sight for this problem, certainly
not one which I think can be devised and implemented simply at this
stage of the cycle. The solution we'd like to use, LWLocks, is not
workable in his context. In consequence, I don't think we have any
option but to shelve this item for the time being.

A couple of bugs have been found and fixes identified, during the review
process, so it's not a total loss, but it is nevertheless a pity that we
can't deliver this feature in 8.3.

cheers

andrew