libpq can now talk to either 3.0 or 2.0 protocol servers. It first tries

libpq can now talk to either 3.0 or 2.0 protocol servers.  It first tries
protocol 3, then falls back to 2 if postmaster rejects the startup packet
with an old-format error message.  A side benefit of the rewrite is that
SSL-encrypted connections can now be made without blocking.  (I think,
anyway, but do not have a good way to test.)