Re: 12.1 not useable: clientlib fails after a dozen queries (GSSAPI ?)

Here's a draft patch that cleans up all the logic errors I could find.

I also expanded the previous patch for the kerberos test so that it
verifies that we can upload a nontrivial amount of data to the server,
as well as download.

I also spent a fair amount of effort on removing cosmetic differences
between the comparable logic in be-secure-gssapi.c and fe-secure-gssapi.c,
such that the two files can now be diff'd to confirm that be_gssapi_write
and be_gssapi_read implement identical logic to pg_GSS_write and
pg_GSS_read. (They did not, before :-(.)

This does not deal with the problem that libpq shouldn't be using
static data space for this purpose. It seems reasonable to me to
leave that for a separate patch.

This passes tests for me, on my FreeBSD build with lo0 mtu = 1500.
It wouldn't hurt to get some more mileage on it though. Peter,
I didn't follow how to set up the "packet radio speed" environment
that you mentioned, but if you could beat on this with that setup
it would surely be useful.

regards, tom lane