Visual Studio 2012 (VS 11) build support by Brar Piening and Noah Misch

This patch introduces handling of the Windows Vista / VS 2012 setlocale()
changes and the altered contents of _locale_t; see comments in
src/backend/utils/adt/pg_locale.c and
http://www.postgresql.org/message-id/20130101025421.GA17763@tornado.leadboat.com

Review and documentation amendments by Craig Ringer