Re: Pasword expiration warning

Here is an updated patch with the units set to seconds.  There are two main
things on my mind:

* The placement of the WARNING.  Right now, I have it placed at the end of
InitPostgres().  There are various other ways to get a WARNING during this
function, so I think it's technically okay, but perhaps it makes more sense
to put it at the end of ClientAuthentication() or something.  But the risk
there is that something between the call to ClientAuthentication() and the
end of InitPostgres() could ERROR/FATAL, in which case our new WARNING
might be giving away more information than necessary.  So, I guess I lean
towards keeping it where it is now, but I would be interested to hear other
opinions on the matter.

* Whether we should emit the warnings for special client backends.
Specifically, I think the current patch will send warnings to logical
replication connections, but not physical replication connections.  My
current feeling is that we should send warnings to any backend that uses a
password to authenticate, i.e., add a call to EmitConnectionWarnings() at
the end of the "am_walsender && !am_db_walsender" block.  Thoughts?  Are
there any other backend types I'm forgetting that would be relevant here?

-- 
nathan