Re: [PATCH v3] GSSAPI encryption support

Alright, here's v3.  As requested, it's one patch now.  Other things
addressed herein include:

 - postgres.h/assert.h ordering fix
 - spacing around casts
 - leaking of GSS buffer in be_gss_inplace_decrypt
 - libpq-be.h not having a conditional internal include
 - always exposing guc veriable gss_encrypt
 - copyright/description headers on all new files
 - movement of GSSAPI methods from fe-auth.c and auth.c to fe-gss.c and
   be-gss.c respectively
 - renaming GSSAPI files to fe-gss.c and be-gss.c (drops -secure)

Andres, one thing you mentioned as "feels rather wrong" was the
GSSAPI-specific code in pqcomm.c; while looking at that again, I have a
slightly better explanation than what I said previously.

Essentially, the problem is that socket_putmessage_noblock() needs to
know the size of the message to put in the buffer but we can't know
that until we've encrypted the message.  socket_putmessage_noblock()
calls socket_putmessage() after ensuring the call will not block;
however, other code paths simply call directly into socket_putmessage()
and so socket_putmessage() needs to have a path to encryption as well.

If you have other potential solutions to this problem, I would love to
hear them; right now though I don't see a better way.

Patch follows.  Thanks!