pgsql: Fix set of NLS translation issues

Fix set of NLS translation issues

While monitoring the code, a couple of issues related to string
translation has showed up:
- Some routines for auto-updatable views return an error string, which
sometimes missed the shot. A comment regarding string translation is
added for each routine to help with future features.
- GSSAPI authentication missed two translations.
- vacuumdb handles non-translated strings.
- GetConfigOptionByNum should translate strings. This part is not
back-patched as after a minor upgrade this could be surprising for
users.

Reported-by: Kyotaro Horiguchi
Author: Kyotaro Horiguchi
Reviewed-by: Michael Paquier, Tom Lane
Discussion: https://postgr.es/m/20180810.152131.31921918.horiguchi.kyotaro@lab.ntt.co.jp
Backpatch-through: 9.3

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/72be8c29a18812975fcc8765a122faf0e4d0c755

Modified Files
--------------
src/backend/commands/tablecmds.c | 2 +-
src/backend/commands/view.c | 2 +-
src/backend/libpq/auth.c | 13 +++++++++++--
src/backend/rewrite/rewriteHandler.c | 9 +++++++++
src/backend/utils/misc/guc.c | 6 +++---
src/bin/scripts/vacuumdb.c | 2 +-
6 files changed, 26 insertions(+), 8 deletions(-)