Tell gettext which codeset to use by calling bind_textdomain_codeset(). We

already did that on Windows, but it's needed on other platforms too when
LC_CTYPE=C. With other locales, we enforce (or trust) that the codeset of
the locale matches the server encoding so we don't need to bind it
explicitly. It should do no harm in that case either, but I don't have
full faith in the PG encoding -> OS codeset mapping table yet. Per recent
discussion on pgsql-hackers.