This is our most common intermittent failure. I don't understand
why it happens and can't reproduce it, but defining an explicit
sort order seems worth a shot...

Intermediate states are unreliable across versions (I think), make
sure we go through the whole connect procedure.

When a connection is closed, we also need to remove the hash entry
from the regular_list, as it now points to freed memory. To do this
store a reverse mapping from the connection to the hash string.

It would be nicer to introduce a wrapping structure for the pgsql
link resource that could store the hash (and notices), but that would
require large changes to the extension, so I'm going for a more
minimal fix here.